Difference between revisions of "JSX"
From MSX Game Library
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== Protocol == | == Protocol == | ||
| − | Proposal for a protocol to handle | + | Proposal for a protocol to handle joypads with a variable number of sticks and buttons, plug in the MSX’s [https://www.msx.org/wiki/General_Purpose_port general purpose port]. |
This protocol can manage joypads with up to 15 analog axis (one stick requires 2 axis) and 18 buttons. | This protocol can manage joypads with up to 15 analog axis (one stick requires 2 axis) and 18 buttons. | ||
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Read R#14 | Read R#14 | ||
: Get 0x0F (JSX idle fingerprint) | : Get 0x0F (JSX idle fingerprint) | ||
| − | : | + | : <u>Note</u>: It could be any value between 00-3F not already return by [https://www.msx.org/wiki/MSX-HID#List_of_known_fingerprints other MSX devices]) |
=== Start communication and get ID === | === Start communication and get ID === | ||
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└─┴─┴─┴────── Number of axis (0-15) | └─┴─┴─┴────── Number of axis (0-15) | ||
</pre> | </pre> | ||
| − | :<u>Note</u>: Number of axis or number of button rows can be zero, but not both. So any device ID is valid except 0x00. | + | :<u>Note</u>: 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 === | === Read bytes === | ||
Latest revision as of 08:45, 23 October 2024
Contents
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.
A pulse on Pin 8 is used to start communication then (while Pin 8 still HIGH) consecutive pulse on Pin 6 is used to synchronize data transmission (6 bits per 6 bits).
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 8: LOW
- Pin 6: any value
Read R#14
- Get 0x0F (JSX idle fingerprint)
- Note: It could be any value between 00-3F not already return by other MSX devices)
Start communication and get ID
Write R#15
- Pin 8: LOW (in case Pin 8 have been modified by another device)
- Pin 6: any value
Write R#15
- Pin 8: HIGH (start communication)
- Pin 6: HIGH
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 8: HIGH
- Pin 6: LOW
Write R#15
- Pin 8: HIGH
- Pin 6: 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