Specifications

Chapter 11
COUNTER/TIMERS (8254)
Contents Page
OVERVIEW .................................................... 11-2
BLOCK DIAGRAM
............................................. 11-3
COUNTER/TIMER ARCHITECTURE
............................ 11-4
OPERATION
................................................... 11-6
Reset State
................................................. 11-6
Programming
............................................... 11-6
Read Operations
............................................. 11-8
Simple Read
............................................ 11-8
Counter Latch Command
................................. 11-8
Read-Back Command
................................... 11-11
Mode Definitions
........................................... 11-16
Mode 0: Interrupt on Terminal Count
..................... 11-16
Mode 1: Hardware Retriggerable One-Shot
............... 11-17
Mode 2: Rate Generator
................................. 11-18
Mode 3: Square Wave Mode
............................. 11-19
Mode 4: Software Triggered Strobe
...................... 11-20
Mode 5: Hardware Triggered Strobe
...................... 11-21
Operation Common to All Modes
............................ 11-23
Programming
.......................................... 11-23
Gate
.................................................. 11-23
Counter
............................................... 11-24
Counter Use by STD DOS and STD ROM
.................... 11-25
11-1