Difference between revisions of "JSX-C"

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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]'''.
 
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''' (3 rows of 6 buttons each).
  
 
Pin 8 is used to synchronize data transmission:
 
Pin 8 is used to synchronize data transmission:
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* then successive pulses on Pin 8 (LOW > HIGH) are used for data transmission (6 bits per 6 bits).
 
* then successive pulses on Pin 8 (LOW > HIGH) are used for data transmission (6 bits per 6 bits).
  
−
* <tt>AX</tt>: Axis number,
+
Pin 6 and 7 are used as input only.
−
* <tt>BR</tt>: Button rows,
+
 
−
* <tt>IN</tt>: Total input number (<tt>= AX + BR</tt>).
+
Internal counter is used to send successive data: first the device ID, then each of the input data.
 +
 
 +
Pin binding for received 6-bit data when reading through R#14:
 +
<syntaxhighlight>
 +
7 6 5 4 3 2 1 0
 +
---------------
 +
0 0 P P P P P P
 +
    │ │ │ │ │ └── Pin 1
 +
    │ │ │ │ └──── Pin 2
 +
    │ │ │ └────── Pin 3
 +
    │ │ └──────── Pin 4
 +
    │ └────────── Pin 6
 +
    └──────────── Pin 7
 +
</syntaxhighlight>
  
 
== States ==
 
== States ==
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Read R#14
 
Read R#14
−
: 6-bit data  
+
: Get 6-bit data  
 +
: Increment the internal counter
  
−
Pin binding for received data:
+
Write R#15
−
<syntaxhighlight>
+
: Pin 8: LOW
−
Bits 7 6 5 4 3 2 1 0
 
−
–-–-–-–-–-–-–-–--–-–-
 
−
Pins x x 7 6 4 3 2 1
 
−
</syntaxhighlight>
 
  
 
==== Device ID ====
 
==== Device ID ====
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First received data is the JSX device ID:
 
First received data is the JSX device ID:
 
<syntaxhighlight>
 
<syntaxhighlight>
−
7 6 5 4 3 2 1 0
+
7 6 5 4 3 2 1 0
−
–-–-–-–-–-–-–-–--
+
---------------
−
0 0 A A A A B B
+
0 0 A A A A B B
−
    │ │ │ │ └─┴── Number of button rows (0-3)
+
    │ │ │ │ └─┴── Number of button rows (0-3)
−
    │ │ │ │        0: No button
+
    │ │ │ │        0: No button
−
    │ │ │ │        1: Up to 6 buttons
+
    │ │ │ │        1: Up to 6 buttons
−
    │ │ │ │        2: Up to 12 buttons
+
    │ │ │ │        2: Up to 12 buttons
−
    │ │ │ │        3: Up to 18 buttons
+
    │ │ │ │        3: Up to 18 buttons
−
    └─┴─┴─┴────── Number of axis (0-15)
+
    └─┴─┴─┴────── Number of axis (0-15)
 
</syntaxhighlight>
 
</syntaxhighlight>
 +
<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.
  
 
Input number can be computed as:
 
Input number can be computed as:
−
* Axis: <tt>ID / 4</tt>
+
* Axis number (<tt>Axies</tt>): <tt>ID >> 2</tt>,
−
* Button rows: <tt>ID & 0x3</tt>
+
* Button rows (<tt>BtnRow</tt>): <tt>ID & 0x03</tt>,
−
* Buttons: <tt>(ID & 0x3) * 6</tt>
+
* Total input number (<tt>TotIn</tt>): <tt>Axies + BtnRow</tt>.
  
−
<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.
+
Repeat data read, for each axis (if any), then for each button row (if any).
 +
The device must be read <tt>TotIn</tt> times to read all data.
  
−
==== Data bytes ====
+
==== Axis data ====
−
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
+
Get 6-bit values
 +
: unsigned 6-bits value [0:63]
  
 +
==== Button row data ====
 
Get 6-bit values
 
Get 6-bit values
−
: For axis: signed 6-bits value [-32 ; 31]
+
: bits field for 6 boutons (0: pressed, 1: released)
−
: For boutons: bits field for 6 boutons (0: pressed, 1: released)
 
  
 
== Example ==
 
== Example ==
 
For a Joypad with a stick with X and Y axis (2 axis), and 4 buttons (1 row), the reading process would be:
 
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.<br/>ID: 0x09 [00 0010 01] for 2 axis, and 1 buttons row,
 
* After starting communication, first read to R#14 return the ID.<br/>ID: 0x09 [00 0010 01] for 2 axis, and 1 buttons row,
−
* Next reading give X-axis value [-32 ; 31],
+
* Next reading give X-axis value [0:63],
−
* Next reading give Y-axis value [-32 ; 31],
+
* Next reading give Y-axis value [0:63],
 
* Next and last reading give button states (for up to 6 boutons).
 
* Next and last reading give button states (for up to 6 boutons).
  
−
[[File:Joystick.png|512px]]
+
[[File:Jsx-c.png|512px]]
  
 
Note: [https://www.msx.org/wiki/MSX-HID MSX-HID] fingerprint would be: 0Fh, 09h, 0Fh
 
Note: [https://www.msx.org/wiki/MSX-HID MSX-HID] fingerprint would be: 0Fh, 09h, 0Fh
  
 
[[Category:Proposal]][[Category:Proposal/Protocol]]
 
[[Category:Proposal]][[Category:Proposal/Protocol]]

Latest revision as of 15:14, 4 November 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 (3 rows of 6 buttons each).

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 input only.

Internal counter is used to send successive data: first the device ID, then each of the input data.

Pin binding for received 6-bit data when reading through R#14: 

7 6 5 4 3 2 1 0
---------------
0 0 P P P P P P
    │ │ │ │ │ └── Pin 1
    │ │ │ │ └──── Pin 2
    │ │ │ └────── Pin 3
    │ │ └──────── Pin 4
    │ └────────── Pin 6
    └──────────── Pin 7

States

Idle state (no-communication)

Write R#15

Pin 8: LOW (for >1 ms)
Reset internal data counter

Read R#14

Get 0x0F (JSX idle fingerprint)
Note: It could be any value between 00-3F not already return by other MSX devices)

Communication state

Write R#15

Pin 8: LOW

Write R#15

Pin 8: HIGH (request data)

Read R#14

Get 6-bit data
Increment the internal counter

Write R#15

Pin 8: LOW

Device ID

First received data is the JSX device ID: 

7 6 5 4 3 2 1 0
---------------
0 0 A A A A B B
    │ │ │ │ └─┴── Number of button rows (0-3)
    │ │ │ │         0: No button
    │ │ │ │         1: Up to 6 buttons
    │ │ │ │         2: Up to 12 buttons
    │ │ │ │         3: Up to 18 buttons
    └─┴─┴─┴────── 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.

Input number can be computed as:

  • Axis number (Axies): ID >> 2,
  • Button rows (BtnRow): ID & 0x03,
  • Total input number (TotIn): Axies + BtnRow.

Repeat data read, for each axis (if any), then for each button row (if any). The device must be read TotIn times to read all data.

Axis data

Get 6-bit values

unsigned 6-bits value [0:63]

Button row data

Get 6-bit values

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 [0:63],
  • Next reading give Y-axis value [0:63],
  • Next and last reading give button states (for up to 6 boutons).

Jsx-c.png

Note: MSX-HID fingerprint would be: 0Fh, 09h, 0Fh

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