NEC PD754144 - Manual (Page 118)

CHAPTER 6 PERIPHERAL HARDWARE FUNCTION
118
User’s Manual U10676EJ3V0UM
6.3.4 Operation as basic interval timer
When WDTM is reset to “0”, the interrupt request flag (IRQBT) is set by the overflow of the basic interval timer
(BT), and the basic interval timer/watchdog timer operates as the basic interval timer. BT is always incremented by
the clock supplied by the clock generator and its counting operation cannot be stopped.
Four time intervals at which an interrupt occurs can be selected by BTM (
µPD754244 only. Refer to Figure 6-
21).
By setting bit 3 of BTM to “1”, BT and IRQBT can be cleared (command to start the interval timer).
The count value of BT can be read by using an 8-bit manipulation instruction. No data can be written to BT.
Start the timer operation as follows (<1> and <2> may be performed simultaneously).
<1> Set interval time to BTM.
<2> Set bit 3 of BTM to “1”.
Example To generate an interrupt at intervals of the µPD754244 of 1.37 ms (at f
X = 6.0 MHz) Note
SET1 MBE
SEL MB15
MOV A, #1111B
MOV BTM, A ; Sets time and starts
EI ; Enables interrupt
EI IEBT ; Enables BT interrupt
Note It is 1.95 ms when the
µPD754244 is operating at f
X = 4.19 MHz.
In the case of the
µPD754144, it is 8.19 ms at f
CC = 1.0 MHz.