Read/Write I/O processor memory

OSWord call Action Available on:
(dec) (hex)BBC Master Electron
5 05 Read I/O processor memory x x x
6 06 Write I/O processor memory x x x

A byte of I/O processor memory may be read or written across the Tube using this call. A 32 bit address should be contained in memory at the address contained in the X and Y registers.

For writes (OSWord 0x06) the value to write should be placed in XY+4

For reads (OSWord 0x05) the value read is placed in XY+4 on exit.

Parameter block

XY+ Content Read call Write call
0 LSB of address in I/O processor
3 MSB of address in I/O processor
4 Byte read by OSWord 0x05 Byte to write with OSWord 0x06

If the I/O processor uses 16 bit memory addressing only least significant two bytes need to be specified.