UPD75238GJ NEC [NEC], UPD75238GJ Datasheet - Page 63

• Manufacturer Part Number: UPD75238GJ
• Description: 4 BIT SINGLE-CHIP MICROCOMPUTER
• Manufacturer: NEC [NEC]

(4) Operation of the basic interval timer
4.5 TIMER/EVENT COUNTER
(1) Functions of the timer/event counter
The basic interval timer (BT) is always incremented by the clock supplied from the clock generator, and
when it overflows, the interrupt request flag (IRQBT) is set. The count operation of BT cannot be stopped.
One of four interrupt generation intervals can be selected by setting BTM. (See Fig. 4-24.)
The basic interval timer and the interrupt request flag can be cleared by setting bit 3 of BTM to 1 (instruction
for starting as an interval timer).
The count status can be read by using an 8-bit manipulation instruction. No data can be loaded to the
timer.
To allow the system clock to stabilize after releasing the STOP mode, a wait function is available which
stops the operation of the CPU until the basic interval timer overflows.
The wait time after a RESET input is fixed. On the other hand, a wait time can be selected by setting BTM
when releasing the STOP mode with an interrupt occurrence. In this case, the wait times are the same
as the interval times shown in Fig. 4-24.
BTM must be set before the STOP mode is set. (For details, see Chapter 6.)
The timer/event counter has the following functions.
Caution
(a) Programmable interval timer operation
(b) Output of a square wave at a given frequency to the PTO0 pin
(c) Event counter operation
(d) Frequency divider operation that divides TI0 pin input by N and outputs the result to the PTO0 pin
(e) Supply of serial shift clock signal to a serial interface circuit
(f) Function of reading the state of counting
When reading the count value of the basic interval timer, execute a read instruction twice so
that unstable data which has been counted will not be read. If the two read values are
reasonable, use the second one as the result. If the two read values are far apart, retry from
the beginning.
PD75238
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