NEC uPD78P078 - Manual (Page 525)

525
CHAPTER 22 INTERRUPT FUNCTIONS
(3) Key return mode register (KRM)
This register is used to set enable/disable of standby function clear by key return signal (port 4 falling edge
detection).
KRM is set with a 1-bit or 8-bit memory manipulation instruction.
RESET input sets KRM to 02H.
Figure 22-21. Key Return Mode Register Format
Caution When port 4 falling edge detection is used, clear KRIF to 0 (not cleared to 0 automatically).
22.5.2 Test input signal acknowledge operation
(1) Internal test signal
If the watch timer overflows, an internal test input signal (INTWT) is generated, by which the WTIF flag is
set. At this time, if it is not masked with the interrupt mask flag (WTMK), a standby release signal is generated.
The watch function is available by checking the WTIF flag at a shorter cycle than the watch timer overflow
cycle.
(2) External test signal
When a falling edge is input to the port 4 (P40 to P47) pins, an external test input signal (INTPT4) is generated,
by which the KRIF flag is set. At this time, if it is not masked with the interrupt mask flag (KRMK), a standby
release signal is generated. If port 4 is used as key matrix return signal input, whether or not a key input
has been applied can be checked from the KRIF status.
7
0
Symbol
KRM
6
0
5
0
4
0
3
0
2
0
<1>
KRMK
<0>
KRIF
Address
FFF6H 02H
After
Reset
R/W
R/W
0
1
Key Return Signal
Not detected
Detected (port 4 rising edge detection)
KRIF
0
1
Standby Mode Control by Key Return Signal
Standby mode release enabled
Standby mode release disabled
KRMK