1. Introduction
13
Memory and I/O Addressing
The ZT 8904 includes 1 Mbyte of system RAM, 1, 2, or 4 Mbytes of Flash, and
128 Kbytes of battery-backed RAM. The battery-backed RAM is not available on the
ZT 8903. System RAM can be expanded from 1 Mbyte to 5 Mbytes with the addition of
an optional memory module. Memory operations up to 16 Mbytes that are not decoded
by local memory devices are directed to the STD bus.
Data transfers are dynamically adjusted to support standard architecture STD bus
memory boards with an 8-bit or 16-bit data path. The memory architecture selected for
the Ziatech Industrial BIOS architecture is shown in the "
Memory Address Map
" in
Chapter 2.
The ZT 8904 also includes many I/O peripherals required for industrial control
applications. I/O operations up to 64 Kbytes not decoded by local I/O devices are
directed to the STD bus. The STD bus I/O expansion signal, IOEXP, is supported to
limit the addressing redundancy of I/O boards decoding fewer than 16 bits of address.
Data transfers are dynamically adjusted to support standard architecture STD bus I/O
boards with an 8-bit or 16-bit data path. A20 is located at port 92h. Set bit 1 to 1 for
disable, 0 for enable. The I/O map architecture selected for the Ziatech Industrial BIOS
architecture is shown in the "
I/O Address Map
".
Local Bus Video
The ZT 8904 supports both STD bus and local bus video adapters. For STD bus video,
Ziatech offers video boards that support VGA and flat panel displays. For local bus
video, Ziatech offers zVID adapters that plug directly onto the ZT 8904 J6 local bus
connector. Local bus video is up to 300% faster than STD bus video because the data
transfers occur at the CPU operating speed of 25 MHz. For space-constrained
applications, the zVID offerings have the added advantage of not requiring the
additional card cage slot needed by the STD bus offerings.
Serial I/O
The ZT 8903 includes two RS-232 serial ports. The ZT 8904 and ZT 89CT04 include
four RS-232 serial ports, two of which can be software configured for RS-485 operation.
COM1 and COM2 are 16C450 compatible UARTs. COM3 and COM4 are 16C550
compatible UARTS. All of the serial ports include a complete set of handshaking and
modem control signals, maskable interrupt generation, and data transfer rates up to
115 Kbaud, and are implemented with a 5 V charge pump technology to eliminate the
need for a ±12 V supply.
The 386 EX multiplexes COM2 data and handshake signals with DMA signals. This
results in the loss of COM2 handshake if STD bus DMA is used and the complete loss
of COM2 if local printer or serial DMA is used. This selection is controlled with jumpers
W24 through W27 and BIOS configuration.
