EM6821 datasheet(14/68 Pages) EMMICRO

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EM6821

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6.2

Port A

The EM6821 has one four bit general purpose CMOS input port. The port A input can be read at any time,

internal pull-up or pull-down resistors can be chosen. All selections concerning port A are bit-wise executable.

I.e. Pull-up on PA[2], pull-down on PA[0], positive IRQ edge on PA[0] but negative on PA[1], etc.

In sleep mode the port A pull-up or pull-down resistors are turned off, and the inputs are deactivated except if

the InpResSleep bit in the option register OPTFSel is set to 1. In this case the port A inputs are continuously

monitored to match the input reset condition which will immediately wake the EM6821 from sleep mode (all pull

resistors remain).

Figure 10. Input Port A Configuration

IntEdgPA[n]=0

NoDebIntPA[n]=1

Mask opt

MPAPU[n]

PA3 for the

Millisecond

Counter

IRQPA[3:0]

PA[n]terminal

PA0, PA3

for 10-Bit

Counter

Mask opt

MPAPD[n]

Debouncer

µP TestVar

Ck[8]

Ck[11] or

Ck[14]

DB[3:0]

NoPullPA[n]

Vbat

(VDD)

VSS

Input Reset allowed

when in Sleep

Sleep

6.2.1 IRQ on Port A

For interrupt request generation (IRQ) one can choose direct or debouncer input and positive or negative edge

IRQ triggering. With the debouncer selected ( OPTDebIntPA ) the input must be stable for two rising edges of

the selected debouncer clock (RegPresc). This means a worst case of 16 ms (default) or 2 ms (0.25 ms by

metal mask) with a system clock of 32 KHz.

Either a positive or a negative edge on the port A inputs - after debouncer or not - can generate an interrupt

request. This selection is done in the option register OPTIntEdgPA.

All four bits of port A can provide an IRQ, each pin with its own interrupt mask bit in the RegIRQMask1 register.

When an IRQ occurs, inspection of the RegIRQ1, RegIRQ2 and RegIRQ3 registers allows the interrupt to be

identified and treated.

At power on or after any reset the RegIRQMask1 is set to 0, thus disabling any input interrupt. A new interrupt

is only stored with the next active edge after the corresponding interrupt mask is cleared. See also the interrupt

chapter 10.

It is recommended to mask the port A IRQ’s while one changes the selected IRQ edge. Else one may generate

a IRQ (Software IRQ). I.e. PA[0] on ‘0’ then changing from positive to negative edge selection on PA[0] will

immediately trigger an IRQPA[0] if the IRQ was not masked.

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