Specifications

Chapter 3
THEORY OF OPERATION
Contents Page
OVERVIEW ..................................................... 3-2
RELATIVE MICROPROCESSOR PERFORMANCE
................ 3-3
STD BUS COMPATIBILITY
...................................... 3-4
MEMORY AND I/O
.............................................. 3-4
SERIAL COMMUNICATIONS
.................................... 3-4
Serial Port 1 (COM1)
......................................... 3-5
Serial Port 2 (COM2)
......................................... 3-6
INTERRUPTS
................................................... 3-8
Interrupt Request Assignments
................................. 3-8
Polled Interrupts on the STD Bus
.............................. 3-10
STD Bus Vectored Interrupts
................................. 3-12
STD Bus Cascaded Interrupts
................................. 3-13
Non-Maskable Interrupts
..................................... 3-14
DIRECT MEMORY ACCESS (DMA)
............................ 3-15
Advantages of DMA
......................................... 3-15
DMA Operation
............................................. 3-16
POWER-FAIL PROTECTION
................................... 3-18
DC Power-Fail
.............................................. 3-18
AC Power-Fail
.............................................. 3-19
System Battery Fail
.......................................... 3-22
BATTERY
..................................................... 3-23
STATUS INDICATOR (LED)
.................................... 3-25
RESET
......................................................... 3-26
CMOS VERSIONS OF THE ZT 8808A/8809A
..................... 3-27
Added Features
............................................. 3-27
Functional Differences
....................................... 3-29
3-1