Control Lines - retrotruestory/M1DEV GitHub Wiki

Control Lines

All control lines are low active. They are:

• IRQ0, IRQ1, IRQ2, IRQ3, IRQ4 and IRQ5 - External interrupt request lines. Highest priority is IRQ0, lowest is IRQ5.
• DMA_REQ - Request control of address and data busses. Assert this line, then wait for DMA_ACK. At that point, you have control of the busses, but must keep DMA_REQ asserted until you're done with them. I expect the front panel to be the only user of this feature.
• DMA_ACK - See above.
• RESET - Asserting this line will cause the following:
• Internal memory address register (MAR) zeroed, which effectively sets PC to 0x0000
• SP zeroed
• Supervisor mode
• Paging off
• Interrupts disabled
• Condition codes (C,S,V,Z) reset
• IRQ0-IRQ5 reset (and internal halt FF reset)
• UARTS reset
• IDE interface reset