Intel 386

vii
CONTENTS
9.3.3 Initialization Command Word 1 (ICW1) ...................................................................9-20
9.3.4 Initialization Command Word 2 (ICW2) ...................................................................9-21
9.3.5 Initialization Command Word 3 (ICW3) ...................................................................9-22
9.3.6 Initialization Command Word 4 (ICW4) ...................................................................9-24
9.3.7 Operation Command Word 1 (OCW1) ....................................................................9-25
9.3.8 Operation Command Word 2 (OCW2) ....................................................................9-26
9.3.9 Operation Command Word 3 (OCW3) ....................................................................9-27
9.3.10 Interrupt Request Register (IRR) ............................................................................9-28
9.3.11 In-Service Register (ISR) ........................................................................................9-28
9.3.12 Poll Status Byte (POLL) ..........................................................................................9-28
9.4 DESIGN CONSIDERATIONS...................................................................................... 9-29
9.4.1 Interrupt Acknowledge Cycle ..................................................................................9-29
9.4.2 Interrupt Detection ..................................................................................................9-29
9.4.3 Spurious Interrupts ..................................................................................................9-30
9.4.4 Cascading Interrupt Controllers ..............................................................................9-30
9.5 PROGRAMMING CONSIDERATIONS........................................................................ 9-32
9.5.1 Interrupt Control Unit Code Examples ....................................................................9-32
CHAPTER 10
TIMER/COUNTER UNIT
10.1 OVERVIEW ................................................................................................................. 10-1
10.1.1 TCU Signals and Registers .....................................................................................10-3
10.2 TCU OPERATION ....................................................................................................... 10-5
10.2.1 Mode 0 – Interrupt on Terminal Count ....................................................................10-6
10.2.2 Mode 1 – Hardware Retriggerable One-shot ..........................................................10-8
10.2.3 Mode 2 – Rate Generator .....................................................................................10-10
10.2.4 Mode 3 – Square Wave ........................................................................................10-12
10.2.5 Mode 4 – Software-triggered Strobe .....................................................................10-16
10.2.6 Mode 5 – Hardware-triggered Strobe ....................................................................10-18
10.3 REGISTER DEFINITIONS......................................................................................... 10-20
10.3.1 Configuring the Input and Output Signals .............................................................10-20
10.3.1.1 Hardware Control of GATE
n ............................................................................10-20
10.3.1.2 Software Control of GATE
n ..............................................................................10-20
10.3.2 Initializing the Counters .........................................................................................10-24
10.3.3 Writing the Counters .............................................................................................10-26
10.3.4 Reading the Counter .............................................................................................10-27
10.3.4.1 Simple Read .....................................................................................................10-27
10.3.4.2 Counter-latch Command ..................................................................................10-27
10.3.4.3 Read-back Command ......................................................................................10-30
10.4 PROGRAMMING CONSIDERATIONS...................................................................... 10-33
10.4.1 Timer/Counter Unit Code Examples .....................................................................10-34