UPD784915B Datasheet, PDF (47/86 Pages) NEC – 16-BIT SINGLE-CHIP MICROCONTROLLERS

µPD784915B, 784916B
3.10 Watch Function
The µPD784916B has a watch function that counts the overflow signals of the watch timer by hardware. As the
clock, the subsystem clock (32.768 kHz) is used.
Because this watch function is independent from the CPU, it can be used even while the CPU is in the standby
mode (STOP mode) or is reset. In addition, this function can be used at a low voltage of VDD = 2.7 V (MIN.).
Therefore, by using only the watch function with the CPU set in the standby mode or reset, a watch operation can
be performed at a low voltage and low current dissipation.
In addition, the watch function can also be used while the CPU is in the normal operation mode, because a dedicated
counter is provided.
The watch function can be used to count up to about 17 years of data.
The hardware watch counters (HW0 and HW1) are shared with external input counters. These counters execute
counting at the falling edge of input to the P65 pin, and can be used to count the HSYNC signals.
Figure 3-25. Block Diagram of Watch Counter
P65
P65
WM.2
(enables/disables operation)
0
13
1
fXT
(32.768 kHz)
Watch
timer
0
Normal
0
1
Fast
forward
WM.1
PM65
PMC65
Edge detection
Pin level read
0
15
HW0
WM.2
(enables/disables operation)
0
13
HW1
WM.2
To NMI generation block
WM.5
WM.4
WM.7
BUZ signal ^WM.6
INTW
47