1. Introduction
15
Timers
Three timers are included on the ZT 8904. Operating modes supported by the timers
include interrupt on count, frequency divider, square wave generator, software
triggered, hardware triggered, and one shot. The number of counter/timers available to
the application programmer depends on the operating system.
For example, the Ziatech MS DOS operating system uses timer 0 to generate system
tick and timer 2 to control the speaker. Timer 1 is available to the application.
See Chapter 5, "
Counter/Timers
" for more information.
DMA
One DMA controller provides two DMA channels for data transfers between local or
system I/O and local memory. DMA channel 0 supports both 8-bit and 16-bit STD bus
DMA slaves. The primary use for STD bus DMA is floppy disk expansion. Optionally,
DMA channel 0 supports the local 1284 parallel port or combines with DMA channel 1 to
support one of the local serial ports.
See Chapter 6, "
DMA Controller
" for more information.
Watchdog Timer
The two-stage watchdog timer optionally monitors system operation. Failure to strobe
the first stage within a programmable time period results in a non-maskable interrupt.
Failure of the non-maskable interrupt service routine to restart the watchdog results in a
stage two reset.
See Chapter 12, "
Watchdog Timer
" for more information.
Real-Time Clock
The real-time clock performs timekeeping functions and includes more than 200 bytes
of general-purpose battery-backed CMOS RAM.
Timekeeping features include an alarm function, a maskable periodic interrupt, and a
100-year calendar.
CMOS RAM available to the application programmer depends on the operating system.
For example, the Ziatech MS DOS operating system uses the CMOS RAM to store
configuration parameters.
See Chapter 7, "
Real-Time Clock
" for more information.