ACE1501VM8 datasheet(21/33 Pages) FAIRCHILD

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ACE1501 Product Family Rev. 1.1

8. Multi-Input Wakeup/Interrupt Block

The

Multi-Input

Wakeup

(MIW)/Interrupt

contains

three

memory-mapped registers associated with this circuit: WKEDG

(Wakeup Edge), WKEN (Wakeup Enable), and WKPND

(Wakeup Pending). Each register has 8-bits with each bit

corresponding to an input pins as shown in Figure 27. All three

registers are initialized to zero upon reset.

The WKEDG register establishes the edge sensitivity for each

of the wake-up input pin: either positive going-edge (0) or

negative-going edge (1).

The WKEN register enables (1) or disables (0) each of the port

pins for the Wakeup/Interrupt function. The wakeup I/Os used

for the Wakeup/Interrupt function must also be conﬁgured as an

input pin in its associated port conﬁguration register. However,

an interrupt of the core will not occur unless interrupts are

enabled for the block via bit 7 of the T0CNTRL register (see Fig-

ure 19) and the G (global interrupt enable) bit of the SR is set.

The WKPND register contains the pending ﬂags corresponding

to each of the port pins (1 for wakeup/interrupt pending, 0 for

wakeup/interrupt not pending). If an I/O is not selected to

become a wakeup input, the pending ﬂag will not be generated.

To use the Multi-Input Wakeup/Interrupt circuit, perform the

steps listed below making sure the MIW edge is selected before

enabling the I/O to be used as a wakeup input thus preventing

false pending ﬂag generation. This same procedure should be

used following any type of reset because the wakeup inputs are

left ﬂoating after resets resulting in unknown data on the port

inputs.

1. Clear the WKEN register.

- CLR WKEN

2. Clear the WKPND register to cancel any pending bits.

- CLR WKPND

3. If necessary, write to the port conﬁguration register to select

the desired port pins to be conﬁgured as inputs.

- RBIT 4, PORTGC

; G4

4. If necessary, write to the port data register to select the

desired port pins input state.

- SBIT 4, PORTGD

; Pull-up

5. Write the WKEDG register to select the desired type of edge

sensitivity for each of the pins used.

- LD

WKEDG, #0FFH

; All negative-going edges

6. Set the WKEN bits associated with the pins to be used, thus

enabling those pins for the Wakeup/Interrupt function.

- LD

WKEN, #10H

; Enabling G4

Once the Multi-Input Wakeup/Interrupt function has been con-

ﬁgured, a transition sensed on any of the I/O pins will set the

corresponding bit in the WKPND register. The WKPND bits,

where the corresponding enable (WKEN) bits are set, will bring

the device out of the HALT mode and can also trigger an inter-

rupt if interrupts are enabled. The interrupt service routine can

read the WKPND register to determine which pin sensed the

interrupt.

The interrupt service routine or other software should clear the

pending bit. The device will not enter HALT mode as long as a

WKPND pending bit is pending and enabled. The user has the

responsibility of clearing the pending ﬂags before attempting to

enter the HALT mode.

Upon reset, the WKEDG register is conﬁgured to select posi-

tive-going edge sensitivity for all wakeup inputs. If the user

wishes to change the edge sensitivity of a port pin, use the fol-

lowing procedure to avoid false triggering of a Wakeup/Interrupt

condition.

1. Clear the WKEN bit associated with the pin to disable that

pin.

2. Clear the WKPND bit associated with the pin.

3. Write the WKEDG register to select the new type of edge

sensitivity for the pin.

4. Set the WKEN bit associated with the pin to re-enable it.

PORTG provides the user with three fully selectable, edge sen-

sitive interrupts that are all vectored into the same service sub-

routine. The interrupt from PORTG shares logic with the wakeup

circuitry. The WKEN register allows interrupts from PORTG to

be individually enabled or disabled. The WKEDG register speci-

ﬁes the trigger condition to be either a positive or a negative

edge. The WKPND register latches in the pending trigger condi-

tions.

Since PORTG is also used for exiting the device from the HALT

mode, the user can elect to exit the HALT mode either with or

without the interrupt enabled. If the user elects to disable the

interrupt, then the device restarts execution from the point at

which it was stopped (ﬁrst instruction cycle of the instruction fol-

lowing HALT mode entrance instruction). In the other case, the

device ﬁnishes the instruction that was being executed when

the part was stopped and then branches to the interrupt service

routine. The device then reverts to normal operation.

Figure 26. Multi-input Wakeup (MIW) Register bit assignments

9. Available only on the 14-pin package option

WKEDG, WKEN, WKPND

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

9 G7

9 G6

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