OSWORD &FF (255) - Z80 Data transfer over Tube (Z80 Tube OS)
On entry: XY?0 =&0D (send block length) XY?1 =&01 (receive block length) XY!2 =I/O address XY!6 =Z80 address XY+10..11=data length XY?12 =command, 0=write to I/O, 1=read from I/O. The control block is not updated on return.
The I/O address at XY!2 accesses the main I/O memory and whichever ROM happens to be paged in when the call is made - usually the current language. An updated version of the OSWORD &FF code uses the full I/O addressing range to access sideways ROMs and both banks of screen memory:
&FFFFxxxx - Main memory &FFFExxxx - Currently displayed screen memory &FFFDxxxx - Shadow screen memory &FFxRxxxx - Sideways ROM/RAM R &FF8xxxxx - VDU workspace RAM
The OSWORD &FF code is available as a *runnable file that can be used with any second processor.
DOS fast screen control (80x86 DOS)
On entry: XY?0 =&00 (send block length) XY?1 =&00 (receive block length)
The control block is ignored, so for speed, set XY?0=0 and XY?1=0.
Commands are sent from the 80x86 via Tube register 2. First, the address is sent, high byte then low byte. This address is updated for the data sent and wraps round from &7FFF to &4000. If the high byte is &00, no low byte is sent, and the routine finishes.
After an address has been sent, a command loop is entered. The command is sent through Tube register 2. Commands are:
- &FF - single byte read through Tube register 1 fills the following eight bytes of screen memory.
- &00 - eight bytes read though Tube register 1 fill following eight bytes of screen memory.
- Other - loop back to wait for address or termination.