NEC PD750008 - Manual (Page 119)

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CHAPTER 5 PERIPHERAL HARDWARE FUNCTIONS
5.3 BASIC INTERVAL TIMER/WATCHDOG TIMER
The µPD750008 contains an 8-bit basic interval timer/watchdog timer, which has the following functions:
(a) Interval timer operation which generates a reference timer interrupt
(b) Operation as a watchdog timer for detecting program crashes and resetting the CPU
(c) Selection of a wait time for releasing the standby mode, and counting
(d) Reading the count value
5.3.1 Configuration of the Basic Interval Timer/Watchdog Timer
Figure 5-23 shows the configuration of the basic interval timer/watchdog timer.
Figure 5-23. Block Diagram of the Basic Interval Timer/Watchdog Timer
Note Instruction execution
5.3.2 Basic Interval Timer Mode Register (BTM)
The BTM is a 4-bit register for controlling operation of the basic interval timer (BT).
A 4-bit memory manipulation instruction is used to set the BTM.
Bit 3 can be independently manipulated using a bit manipulation instruction.
Example The interrupt generation interval is set to 1.37 ms (at 6.00 MHz).
SEL MB15 ; or CLR1 MBE
MOV A,#1111B
MOV BTM,A ; BTM <– 1111B
From the clock
generator
Internal bus
4
f X /2
5
f
X
/2
7
f X /2
9
f X /2
12
MPX
Basic interval timer
(8-bit frequency divider)
Clear signal Clear signal
BT interrupt
request flag
Vectored
interrupt
request
signal
IRQBT
Wait release
signal for standby
release
Set
signal
BT
8
BTM3 BTM2 BTM1 BTM0 BTM
SET1
Note
3
1
WDTM
Internal
reset signal
SET1
Note