Some Coleco docs
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ColecoVision Sound Generation Hardware
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The ColecoVision uses the Texas Instruments SN76489A sound
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generator chip. It contains three programmable tone generators,
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each with its own programmable attenuator, and a noise source
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with its own attenuator.
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1. Tone Generators
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Each tone generator consists of a frequency synthesis section
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requiring ten bits of information to define half the period of
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the desired frequency (n). F0 is the most significant bit and
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F9 is the least significant bit. The information is loaded into
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a ten stage tone counter, which is decremented at a N/16 rate
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where N (3.579MHz) is the input clock frequency. When the tone
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counter decrements to zero, a borrow signal is produced. This
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borrow signal toggles the frequency flip-flop and also reloads
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the tone counter. Thus, the period of the desired frequency is
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twice the value of the period register.
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The frequency can be calculated by the following:
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f = 3.579MHz/(32n)
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The output of the frequency flip-flop feeds into a four stage
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attenuator. The attenuator values, along with their bit position
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in the data word, are shown below. Multiple attenuation control
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bits may be true simultaneously. THus, the maximum attenuation
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is 28 db.
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A0 A1 A2 A3 Weight
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0 0 0 1 2 db
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0 0 1 0 4 db
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0 1 0 0 8 db
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1 0 0 0 16 db
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1 1 1 1 Off
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2. Noise Generator
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The noise generator consists of a noise source that is a
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shift register with an exclusive OR feedback network. The
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feedback network has provisions to protect the shift register
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from being locked in the zero state.
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Noise Feedback Control
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FB Configuration
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0 "Periodic" Noise
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1 "White" Noise
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Noise Generator Frequency Control
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NF0 NF1 Shift Rate
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0 0 N/512
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0 1 N/1024
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1 0 N/2048
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1 1 Tone gen #3 output
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3. Control Registers
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The SN76489A has eight internal registers which are used
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to control the three tone generators and the noise source.
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During all data transfers to the SN76489A, the first byte
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contains a three bit field which determines the destination
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control register. The register address codes are shown here.
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Register Address Field
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R0 R1 R2 Destination Control Register
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0 0 0 Tone 1 Frequency
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0 0 1 Tone 1 Attenuation
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0 1 0 Tone 2 Frequency
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0 1 1 Tone 2 Attenuation
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1 0 0 Tone 3 Frequency
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1 0 1 Tone 3 Attenuation
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1 1 0 Noise Control
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1 1 1 Noise Attenuation
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4. Data Formats
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The formats required to transfer data are shown below.
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Frequency
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LSB MSB LSB MSB
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+---+--------+-----------+ +---+---+-----------------+
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| |Reg Addr| Data | | | | Data |
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+ 1 +--+--+--+--+--+--+--+ | 0 | X +--+--+--+--+--+--+
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| |R0|R1|R2|F6|F7|F8|F9| | | |F0|F1|F2|F3|F4|F5|
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+---+--+--+--+--+--+--+--+ +---+---+--+--+--+--+--+--+
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Noise Control
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LSB MSB
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+---+---+---+---+---+----+-------+
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| | Reg Addr | | | Shift |
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+ 1 +---+---+---+ X | FB +---+---+
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| | 1 | 1 | 0 | | |NF0|NF1|
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+---+---+---+---+---+----+---+---+
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Attenuator
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LSB MSB
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+---+--------+-----------+
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| |Reg Addr| Data |
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+ 1 +--+--+--+--+--+--+--+
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| |R0|R1|R2|A0|A1|A2|A3|
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+---+--+--+--+--+--+--+--+
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Coleco Vision Cart Info
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-----------------------
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All carts start at 8000h with a header that tells the BIOS what to do.
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8000 - 8001: If bytes are AAh and 55h, the CV will show a title screen
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and game name, etc.
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If bytes are 55h and AAh, the CV will jump directly to the
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start of code vector.
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8002 - 8003: Vector; ??? --\
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\
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8004 - 8005: Vector; ??? \
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>--- These always point to 0000 or RAM (7xxx)
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8006 - 8007: Vector; ??? /
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/
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8008 - 8009: Vector; ??? --/
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800A - 800B: Vector; Start of code
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800C - 800E: Jmp to: RST 08h
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800F - 8011: Jmp to: RST 10h
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8012 - 8014: Jmp to: RST 18h
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8015 - 8017: Jmp to: RST 20h
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8018 - 801A: Jmp to: RST 28h
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801B - 801D: Jmp to: RST 30h
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801E - 8020: Jmp to: RST 38h
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8021 - 8023: JMP to: NMI (Vertical Blanking Interrupt from video chip)
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8024 - nnnn: Title screen data:
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Data for the title screen is composed of 4 lines in the format:
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+--------------+
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| COLECOVISION |
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| |
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| LINE 2 |
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| LINE 3 |
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|(c)xxxx COLECO|
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+--------------+
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Typical Screen
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The 'ColecoVision' line cannot be changed, as well as the '(C)xxxx Coleco'
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part of the bottom line. Only the xxxx part can be changed.
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The data is stored as one string with the '/' character (2Fh) used as a
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delimiter. It signals the end of a line, and isn't printed.
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The lines are stored out of order like so:
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"LINE 3/LINE 2/xxxx" There isn't an end-of-line delimiter, because the
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last line is always 4 characters (it's meant for a year like 1983)
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So, if we want to see the following:
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+--------------+
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| COLECOVISION |
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| |
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| MY GAME! |
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| BY: ME |
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|(c)1995 COLECO|
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+--------------+
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We would use the string:
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"BY: ME!/MY GAME!/1995"
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Remember, we cannot change the "(c)xxxx COLECO" part, only the xxxx in the
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middle of the line.
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The lines are self-centering on the screen.
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Altho the BIOS ROM has both upper-case and lower-case characters in the
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character set, only upper-case is supported.
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All printable characters are based on the ASCII character set:
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(all values in hex)
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00-1C: Blank
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1D : (c) (Copyright symbol)
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1E-1F: tm (TradeMark symbol, uses 2 chars side-by-side)
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20-2E: (respectively) space ! " # $ % & ' ( ) * + , - .
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2F : Delimiter- used to end a line, not printable
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30-39: 0-9
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3A-40: (respectively) : ; < = > ? @
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41-5A: A-Z
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5B-5F: (respectively) [ \ ] ^ _
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The chars # 60-8F are the 4-char blocks that make up the 'COLECOVISION'
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name at the top, arranged like so:
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6062 6466 686A 6C6E 7072 7476 787A 7C7E 8082 8486 888A 8C8E
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6163 6567 696B 6D6F 7173 7577 797B 7D7F 8183 8587 898B 8D8F
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C O L E C O V I S I O N
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(purple) (orange) (pink) (yellow) (green) (blue)
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What's intresting, is when these are in the title lines, they show up in
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their respective colours! All other printable chars are white.
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Chars 90-FF are all blank
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Controls:
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---------
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There are 4 ports governing the operation of the controls. They are:
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80- When written to, enables the keypads and right buttons on both controls.
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C0- When written to, enables the joysticks and left buttons on both controls.
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These 2 ports toggle a flip-flop, so the data going out the ports
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is irrelevant.
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FC- Reading this port gives the status of controller #1. (farthest from front)
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FF- Reading this one gives the status of controller #2. (closest to front)
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All switch closures are represented by a '0' Open switches are '1'
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Only 5 bits of ports FC and FF are used:
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'80' mode (port 80 written to)
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bit #6= status of right button
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The keypad returns a 4-bit binary word for a button pressed:
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bit #
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btn: 0 1 2 3
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-----------------------
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0 0 1 0 1
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1 1 0 1 1
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2 1 1 1 0
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3 0 0 1 1
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4 0 1 0 0
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5 1 1 0 0
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6 0 1 1 1
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7 1 0 1 0
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8 1 0 0 0
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9 1 1 0 1
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* 1 0 0 1
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# 0 1 1 0
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Re-arranged, in order:
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btn: 0 1 2 3 hex#
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-------------------------------
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inv. 0 0 0 0 0
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8 1 0 0 0 1
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4 0 1 0 0 2
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5 1 1 0 0 3
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inv. 0 0 1 0 4
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7 1 0 1 0 5
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# 0 1 1 0 6
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2 1 1 1 0 7
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inv. 0 0 0 1 8
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* 1 0 0 1 9
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0 0 1 0 1 A
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9 1 1 0 1 B
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3 0 0 1 1 C
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1 1 0 1 1 D
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6 0 1 1 1 E
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inv. 1 1 1 1 F (No buttons down)
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The controllers have 28 diodes in them that generate the above table.
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Coleco did this so the programmer wouldn't have to scan the keys. Also,
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there wouldn't have been enough pins on the end of the cable to accomodate
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the array. (There are only 7 pins on the connector. That's just enough
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to scan a 3*4 matrix, but that doesn't include the stick or other 2
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buttons.)
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'C0' mode (port C0 written to)
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This mode allows you to read the stick and left button:
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Bit 6=Left button
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Bit 0=Left
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Bit 1=Down
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Bit 2=Right
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Bit 3=Up
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CV's memory/IO map
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------------------
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The CV uses 2 74138 3-8 line decoders to generate the memory and IO maps.
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As you would expect, memory is broken up into 8 8K blocks. However, the IO
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map is broken up into 4 write and 4 read ports.
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Memory:
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(ABC lines of decoder go to A5, A6, and A7 respectively /E1 -> /M_request
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/E2 -> Reset; E3 -> +V)
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0000-1FFF = BIOS ROM
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2000-3FFF = Expansion port
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4000-5FFF = Expansion port
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6000-7FFF = SRAM (1K)
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8000-9FFF = Cart
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A000-BFFF = Cart
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C000-DFFF = Cart
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E000-FFFF = Cart
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IO:
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(ABC lines of decoder go to /WR, A5, and A6 respectively /E1 -> /IO_request
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/E2 -> Reset; E3 -> A7)
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80-9F (W) = Controls _ Set to keypad mode
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80-9F (R) = Not Connected
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A0-BF (W) = Video \___ A0 also decoded by video chip
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A0-BF (R) = Video /
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C0-DF (W) = Controls _ Set to joystick mode
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C0-DF (R) = Not Connected
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E0-FF (W) = Sound
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E0-FF (R) = Controls _ A1 also decoded by chips (A1=0 ctrl 1; A1=1 ctrl 2)
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CV's sound chip
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---------------
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The sound chip in the CV is a SN76489AN manufactured by Texas Instruments.
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It has 4 sound channels- 3 tone and 1 noise.
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The volume of each channel can be controlled seperately in 16 steps from
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full volume to silence.
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A byte written into the sound chip determines which register is used, along
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with the frequency/ attenuation information.
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The frequency of each channel is represented by 10 bits. 10 bits won't
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fit into 1 byte, so the data is written in as 2 bytes.
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Here's the control word:
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+--+--+--+--+--+--+--+--+
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|1 |R2|R1|R0|D3|D2|D1|D0|
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+--+--+--+--+--+--+--+--+
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1: This denotes that this is a control word
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R2-R0 the register number:
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000 Tone 1 Frequency
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001 Tone 1 Volume
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010 Tone 2 Frequency
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011 Tone 2 Volume
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100 Tone 3 Frequency
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101 Tone 3 Volume
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110 Noise Control
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111 Noise Volume
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D3-D0 is the data
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Here's the second frequency register:
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+--+--+--+--+--+--+--+--+
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|0 |xx|D9|D8|D7|D6|D5|D4|
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+--+--+--+--+--+--+--+--+
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0: This denotes that we are sending the 2nd part of the frequency
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D9-D4 is 6 more bits of frequency
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To write a 10-bit word for frequenct into the sound chip you must first
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send the control word, then the second frequency register. Note that the
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second frequency register doesn't have a register number. When you write
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to it, it uses which ever register you used in the control word.
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So, if we want to output 11 0011 1010b to tone channel 1:
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First, we write the control word:
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LD A,1000 1010b
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OUT (F0h),A
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Then, the second half of the frequency:
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LD A,0011 0011b
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OUT (F0h),A
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To tell the frequency of the wave generated, use this formula:
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3579545
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f= -------
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32n
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Where f= frequency out,
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and n= your 10-bit binary number in
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To control the Volume:
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+--+--+--+--+--+--+--+--+
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|1 |R2|R1|R0|V3|V2|V1|V0|
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+--+--+--+--+--+--+--+--+
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R2-R0 tell the register
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V3-V0 tell the volume:
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0000=Full volume
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.
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.
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.
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1111=Silence
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The noise source is quite intresting. It has several modes of operation.
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Here's a control word:
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+--+--+--+--+--+--+--+--+
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|1 |1 |1 |0 |xx|FB|M1|M0|
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+--+--+--+--+--+--+--+--+
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FB= Feedback:
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0= 'Periodic' noise
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1= 'white' noise
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The white noise sounds, well, like white noise.
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The periodic noise is intresting. Depending on the frequency, it can
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sound very tonal and smooth.
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M1-M0= mode bits:
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00= Fosc/512 Very 'hissy'; like grease frying
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01= Fosc/1024 Slightly lower
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10= Fosc/2048 More of a high rumble
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11= output of tone generator #3
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You can use the output of gen. #3 for intresting effects. If you sweep
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the frequency of gen. #3, it'll cause a cool sweeping effect of the noise.
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The usual way of using this mode is to attenuate gen. #3, and use the
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output of the noise source only.
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The attenuator for noise works in the same way as it does for the other
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channels.
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Video
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-----
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The CV uses a TMS9918a chip made by Texas Instruments.
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