D17133CS datasheet(135/289 Pages) NEC

135 / 289 page

CHAPTER 13

PERIPHERAL HARDWARE

120

13.1.3 Operation of 8-bit Timer Counters

(1) Count Register

Count register are 8-bit up counters whose initial values are 00H. They are incremented each time a count

pulse is entered.

The counter register is initialized in the following situations:

• when the microcontroller is reset (refer to CHAPTER 6 RESET);

• when the content of the 8-bit modulo register coincides with the count register value, thus causing the

comparator to generate the relevant signal; and

• when "1" is written in the TMRES of the register file.

(2) Modulo register

The modulo registers determine the count value of count register. They are initialized to FFH.

A value is set in a modulo register via the data buffer (DBF) using the PUT instruction.

(3) Comparator

The comparators output match signals when the value of the count register and modulo register match and

when the next count pulse is input. That is, if the value of the modulo register is initial value FFH, the

comparator outputs a match signal when 256 is counted.

The match signal from the comparator clears the contents of the count register to 0 and automatically sets

the interrupt request flag (IRQTM) to 1. At this time interrupt handling occurs if the EI instruction (interrupt

acceptance enable instruction) is executed and also the interrupt enable flag (IPTM) is set. When an interrupt

is accepted, the interrupt request flag (IRQTM) is set to 0 and program control transfers to the interrupt

handling routine.

13.1.4 Selecting Count Pulse

A count pulse is selected with TMCK0 or TMCK1.

One system clock fX can be selected from four types: a 2048-count pulse, 256-count pulse, 32-count pulse, and

an external count pulse input from the INT pin.

At reset, TMCK0 and TMCK1 are 0 and fX/256 is selected.

At power start-up or reset, timer is used to generate stabilization wait time. For this purpose, the initial values

are TMCK0=0 and TMCK1=0 and fX/256 is selected. Since the initial value is set to TMEN=1, the system starts at

address 0000H after 8 ms after reset at fX=8 MHz (32 ms at fX=2 MHz). (Refer to CHAPTER 16 RESET.)

D17133CS Datasheet(PDF) 135 Page - NEC