GMS81C2012 datasheet(43/107 Pages) HYNIX

43 / 107 page

HYUNDAI MicroElectronics

GMS81C2012/GMS81C2020

MAR. 2000 Ver 1.00

10. BASIC INTERVAL TIMER

The GMS81C20xx has one 8-bit Basic Interval Timer that

is free-run, can not stop. Block diagram is shown in Figure

10-1. In addition, the Basic Interval Timer generates the

time base for watchdog timer counting. It also provides a

Basic interval timer interrupt (BITIF).

The 8-bit Basic interval timer register (BITR) is increased

every internal count pulse which is divided by prescaler.

Since prescaler has divided ratio by 8 to 1024, the count

rate is 1/8 to 1/1024 of the oscillator frequency. As the

count overflows from FFH to 00H, this overflow causes to

generate the Basic interval timer interrupt. The BITIF is in-

terrupt request flag of Basic interval timer. The Basic In-

terval Timer is controlled by the clock control register

(CKCTLR) shown in Figure 10-2.

When write "1" to bit BTCL of CKCTLR, BITR register is

cleared to "0" and restart to count-up. The bit BTCL be-

comes "0" after one machine cycle by hardware.

If the STOP instruction executed after writing "1" to bit

WAKEUP of CKCTLR, it goes into the wake-up timer

mode. In this mode, all of the block is halted except the os-

cillator, prescaler (only fXIN

÷2048) and Timer0.

If the STOP instruction executed after writing "1" to bit

RCWDT of CKCTLR, it goes into the internal RC oscillat-

ed watchdog timer mode. In this mode, all of the block is

halted except the internal RC oscillator, Basic Interval

Timer and Watchdog Timer. More detail informations are

explained in Power Saving Function. The bit WDTON de-

cides Watchdog Timer or the normal 7-bit timer.

Source clock can be selected by lower 3 bits of CKCTLR.

BITR and CKCTLR are located at same address, and ad-

dress 0ECH is read as a BITR, and written to CKCTLR.

Figure 10-1 Block Diagram of Basic Interval Timer

MUX

Basic Interval

BITR

Select Input clock 3

Basic Interval Timer

source

clock

8-bit up-counter

BTS[2:0]

BTCL

÷1024

÷512

÷256

÷128

÷64

÷32

÷16

÷8

To Watchdog timer (WDTCK)

CKCTLR

clear

overflow

Internal bus line

clock control register

[0ECH]

BITIF

Read

XIN PIN

Timer Interrupt

Internal RC OSC

RCWDT

WAKEUP

STOP

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