Difference between revisions of "JSX-B"
From MSX Game Library
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Pin 6 and 7 are used as 2-bit transfer mode identifier: | Pin 6 and 7 are used as 2-bit transfer mode identifier: | ||
| − | * <tt>00</tt>: | + | * <tt>00</tt>: ''Reserved'' |
| − | * <tt>01</tt>: | + | * <tt>01</tt>: ''Reserved'' |
| − | * <tt>10</tt>: | + | * <tt>10</tt>: Get Device ID |
| − | * <tt>11</tt>: | + | * <tt>11</tt>: Serial read of joypad input data (and increment internal counter) |
Pin binding for received data: | Pin binding for received data: | ||
Latest revision as of 13:35, 31 October 2024
Protocol
Proposal for a protocol to handle joypads with a variable number of sticks and buttons, plug in the MSX’s general purpose port.
This protocol can manage joypads with up to 15 analog axis (one stick requires 2 axis) and 18 buttons.
Pin 8 is used to synchronize data transmission:
- Leaving Pin 8 LOW for long enough (>1 ms, about 3580 t-states) resets the joystick's internal counter,
- then successive pulses on Pin 8 (LOW > HIGH) are used for data transmission (6 bits per 6 bits).
Pin 6 and 7 are used as 2-bit transfer mode identifier:
- 00: Reserved
- 01: Reserved
- 10: Get Device ID
- 11: Serial read of joypad input data (and increment internal counter)
Pin binding for received data:
Bits 7 6 5 4 3 2 1 0 –-–-–-–-–-–-–-–--–-–- Pins x x 7 6 4 3 2 1
States
No-communication state
Write R#15
- Pin 6: any value
- Pin 7: any value
- Pin 8: LOW (for >1 ms)
Read R#14
- Get 0x11 (JSX idle fingerprint)
- Note: It could be any value between 00-3F not already return by other MSX devices)
Device ID
Write R#15
- Pin 6: any value
- Pin 7: any value
- Pin 8: LOW (for >1 ms)
Write R#15
- Pin 6: LOW
- Pin 7: LOW
- Pin 8: HIGH (send device ID)
Read R#14
- Get JSX device ID
7 6 5 4 3 2 1 0
–-–-–-–-–-–-–-–--
x x A A A A B B
│ │ │ │ └─┴── Number of button rows (0-3)
└─┴─┴─┴────── Number of axis (0-15)
- Note: Number of axis or number of button rows can be zero, but not both. So any device ID up to 0x3F is valid except 0x00.
Read bytes
Repeat this step for each axis (if any), then for each button row (if any). Number of axis and button rows is given by the device ID
Write R#15
- Pin 6: any value
- Pin 7: any value
- Pin 8: LOW
- Pin 8 have to stay LOW for more than 1 ms for the first read, then less than 1 ms for the next ones
Write R#15
- Pin 6: HIGH
- Pin 7: LOW
- Pin 8: HIGH
Read R#14
- Get 6-bits values
- For axis: signed 6-bits value [-32 ; 31]
- For boutons: bits field for 6 boutons (0: pressed, 1: released)
Example
For a Joypad with a stick with X and Y axis (2 axis), and 4 buttons (1 row), the reading process would be:
- After starting communication, first read to R#14 return the ID.
ID: 0x09 [00 0010 01] for 2 axis, and 1 buttons row, - Next reading give X-axis value [-32 ; 31],
- Next reading give Y-axis value [-32 ; 31],
- Next and last reading give button states (for up to 6 boutons).
Note: MSX-HID fingerprint would be: 0Fh, 09h, 0Fh