8XC196MC, MD, MH USER’S MANUAL

The protection circuitry (Figure 9-3) monitors the EXTINT pin. When it detects a valid event on the input, it simultaneously disables the outputs and generates an EXTINT interrupt request. Soft- ware can also disable the outputs by clearing the enable outputs (EO) bit in the protection (WG_PROTECT) register.

For the 8XC196MC and 8XC196MD, disabled outputs go to their inactive states based on the programmed polarity. The protection circuitry of the 8XC196MH operates in the same way as that of the 8XC196MC and 8XC196MD, but it allows you to choose the method used to disable the outputs. It can either place outputs in their inactive states, as the other devices do, or it can apply weak pull-ups to them. The protection type (PT) bit in the protection register controls the method.

 

 

 

ES, IT

 

 

 

 

 

EXTINT

 

 

 

 

 

Interrupt

DP

 

 

 

 

Request

 

 

 

 

 

EO Bit

 

 

Falling

 

 

Register

 

 

00

Pulse

 

 

Transition

 

 

 

 

 

 

 

 

Detector

Rising

01

 

R

 

 

 

 

OD#

EXTINT

 

 

 

 

 

 

 

 

Q

 

 

Low

10

 

 

 

Level

 

 

S

 

 

 

 

FXTAL1

Sampler

High

11

 

 

 

 

 

 

 

 

 

 

CPU Write EO

CPU Read EO

 

 

 

 

CPU Bus

 

 

 

 

 

 

A2661-01

Figure 9-3. Protection Circuitry

9.3.4Register Buffering and Synchronization

The WG_RELOAD, WG_COMPx, and WG_OUTPUT registers are buffered; you read and write the buffers rather than the registers. The waveform generator updates the registers synchronously to prevent erroneous or nonsymmetrical duty cycles.

When you write to the WG_COMPx buffers while the counter is stopped (either when the counter register is zero or when the enable counter bit in the control register is clear), the registers are updated one-half state time later.

9-6

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Intel 8XC196MH, 8XC196MD, 8XC196MC manual Register Buffering and Synchronization, Protection Circuitry