Tandy 1000 HX - Page 33

• TANDY COMPUTER PRODUCTS -
Interrupt Function
The 8088 supports two types of interrupts: maskable (by the
CPU, INT) and non-maskable (NMD. See Figure 8. The 8259A
Interrupt Controller is the source of the INT for the 8088.
The 8259A has eight interrupt inputs controlled through
software commands. It can mask (disable) and prioritize
(arrange priority) to the inputs which can generate INT.
These eight interrupts are:
The NMI interrupt is not maskable by the CPU but it can be
enabled/disabled by hardware. The enable is at Port 00A0
Bit 7. The enable is cleared by RESET. There is no
specific function assigned to NMI and it is available on the
bus.
28
#0
#1
#2
#3
#4
#5
#6
#7
Timer Channel 0
Keyboard
Hard Disk Controller
Comm 2
Comm 1
Vertical Sync
Disk Controller, Floppy
Printer
Software Timer
Keyboard Code Received
Optional Function, Interrupt
on Bus
Optional Function, Interrupt
on Bus
Optional Function, Interrupt
on Bus
Software Timer for Video
Ready to Receive/Transmit
Data
Data Transmission Complete