8. Serial Controller
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Address Mapping
The address mapping for the PC standard architecture and the ZT 8904 is shown
below.
Serial Channel
PC Port Address
ZT 8904 Port Address
COM1
3F8-3FF
3F8-3FF
COM2
2F8-2FF
2F8-2FF
COM3
3E8-3EF
2E0-2E7
COM4
2E8-2EF
2E8-2EF
Interrupt Selection
The interrupt mapping for the PC standard architecture and the ZT 8904 is shown
below. Different interrupt levels for COM3 and COM4 interrupts are selectable through
the interrupt jumper block.
Serial Channel
PC Interrupt
ZT 8904 Interrupt
COM1
IR4
IR4
COM2
IR3
IR3
COM3
IR4
IR13
COM4
IR3
IR9
Handshake Signals
The PC architecture includes Transmit Data (TXD), Receive Data (RXD), Request To
Send (RTS), Clear To Send (CTS), Data Set Ready (DSR), Data Terminal Ready
(DTR), Ring Indicator (RI), and Data Carrier Detect (DCD). The ZT 8904 COM1, COM3,
and COM4 channels include a complete set of PC architecture signals.
The ZT 8904 COM2 channel shares TXD, RXD, CTS, and DCD with DMA channels 0
and 1 as selected with jumpers W24-W27 and COM2 BIOS configuration. The
restrictions imposed by this sharing are that COM2 is not available if printer DMA is
enabled and that COM2 is available without CTS and DCD handshake lines if STD Bus
DMA is enabled (for example, if an STD Bus floppy disk is installed).