User manual

8. Serial Controller
76
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).