Intel 386 Manuale Utente Scaricare il pdf (Pagina 251)

100

101

Intel386™ EX EMBEDDED PROCESSOR USER’S MANUAL

10-8

Figure 10-4 shows writing a new count before the current count reaches zero. The counter loads

the new count on the CLKINn pulse after you write it, then decrements this new count on each

succeeding CLKINn pulse. OUTn remains low until the new count reaches zero.

Figure 10-4. Mode 0 – Writing a New Count

10.2.2 Mode 1 – Hardware Retriggerable One-shot

This mode is similar to mode 0; it allows you to generate a rising edge on a counter’s OUTn sig-

nal. Unlike mode 0, however, the counter waits for a gate-trigger before loading the count and

driving its OUTn signal low. When the counter reaches zero, OUTn is driven high. At this point,

the counter rolls over and continues counting with OUTn high. OUTn stays high and keeps count-

ing down and rolling over until the counter receives another gate-trigger or you reprogram it. You

can retrigger the one-shot at any time with a gate-trigger, causing the counter to reload the count

and drive OUTn low. Writing a new control word to the counter reprograms it.

Mode 1’s basic operation is outlined below and shown in Figure 10-5.

1. After a control word write, OUTn is driven high.

2. On the CLKINn pulse following a gate-trigger, the count is loaded and OUTn is driven

low.

3. On each succeeding CLKINn pulse, the count is decremented.

4. When the count reaches zero, OUTn is driven high.

NOTE

Writing a count of N causes a rising edge on OUTn in N CLKINn pulses after

the count is loaded (using a gate-trigger).

Writes to

Counter

CLKIN

GATE

OUT

????0003 0002 0001 0002 0001 0000 FFFF

Control

Word = 10H

Count

Count = 2

Count = 3

A2395-02

1 2 ... 246 247 248 249 250 251 252 253 254 255 256 ... 690 691

Commenti su questo manuale

Nessun commento

Intel 386 Manuale Utente Pagina 251

Commenti su questo manuale

Prodotti e manuali riguardandi Hardware Intel 386