Joystick I/O Mode
From SpecNext official Wiki
| Number | $0B |
|---|---|
| Readable | Yes |
| Writable | Yes |
| Short Description | Joystick port I/O control |
bit 7 = 1 to enable i/o mode (soft reset = 0)
bit 6 = Reserved, must be 0
bits 5:4 = I/O Mode (soft reset = 0)
00 = bit bang
01 = clock
10 = uart on left joystick port
11 = uart on right joystick port
bits 3:1 = Reserved, must be 0
bit 0 = Parameter (soft reset = 1)
bit bang : copied to pin 7
clock : 0 = hold high when clock becomes high, 1 = run *
uart : 0 = redirect esp uart0 to joystick, 1 = redirect pi uart1 to joystick
(Tx out on pin 7, Rx in from pin 9, CTS_n in from pin 6 **)
The state of output pin 7 is stored internally in a register and is retained across changing modes and while i/o mode is disabled. While in i/o mode, keyboard joystick types (Sinclair, Cursor, etc) produce no readings but the current state of pins can still be read via the Kempston ports. When leaving i/o mode, joystick operation resumes after ~64 scan lines have passed.
* CTC channel 3 is currently used to drive pin 7 in clock mode. Freq = Fctc3 / 2. ** CTS_n is only active if the seleced uart is in hw flow control mode.