Introduction
Real-Time Clock
The real-time clock on the ZT 8809A is a Dallas Semiconductor
DS 1215. It keeps track of hundredths of seconds, seconds, minutes,
hours, days, date of the month, months, and years. The clock
automatically corrects for leap years, and adjusts for months with
fewer than 31 days. It may be battery-backed by the optional battery.
The real-time clock shares its address space with the 32 Kbyte static
RAM. To communicate with the DS 1215, a 64-bit signature must be
written to the device, which then switches out the 32 Kbyte static
RAM and switches in the timekeeper function.
Serial Communications
The
ZT 8809A
contains
two
asynchronous
RS-232-C
communications channels, one of which is selectable for RS-422/485.
Both use the same type of UART chip (16C450 equivalent), which is
functionally equivalent to the serial communications channels found
in the IBM family of personal computers or their compatibles.
Each channel has a programmable baud rate generator, loopback
diagnostic capability, maskable interrupt generation, and jumper
selectable DCE or DTE configuration. The two channels become the
COM1 and COM2 serial ports in an STD DOS system. All drivers for
both the RS-232-C and RS-422/485 are on board the ZT 8809A.
COM2 may be disabled to allow an external board, such as a modem
board, to provide COM1.
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