Intel 386 Manuale Utente Scaricare il pdf (Pagina 261)

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101

Intel386™ EX EMBEDDED PROCESSOR USER’S MANUAL

10-18

10.2.6 Mode 5 – Hardware-triggered Strobe

Initializing a counter for mode 5 sets the counter’s OUTn signal, starting the counting sequence.

A gate-trigger loads the programmed count. When the counter reaches zero, OUTn strobes low

for one clock pulse. The counter then rolls over and continues counting, but OUTn does not strobe

low when the count reaches zero. The OUTn strobes low only the first time it reaches zero after

a count is loaded.

Mode 5’s basic operation is outlined below and shown in Figure 10-19.

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

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

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

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

5. On the following CLKINn pulse, OUTn is driven high.

NOTE

Writing a count of N causes OUTn to strobe low N + 1 CLKINn pulses after

the counter receives a gate-trigger. OUTn remains low for one CLKINn pulse,

then goes high.

Figure 10-19. Mode 5 – Basic Operation

A2316-01

? ? ? ? ? 0003 0002 0001 0000 FFFF 0003

Writes to

Counter

CLKIN

GATE

OUT

Control

Word = 1AH

Count

0002 0001 0000

Count = 3

1 2 ... 256 257 258 259 260 261 262 263 264 265 266 ... 690 691

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Intel 386 Manuale Utente Pagina 261

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