
GMS81C1404/GMS81C1408
June. 2001 Ver 1.2
41
12. Basic Interval Timer
The GMS81C1404 and GMS81C1408 has one 8-bit Basic
Interval Timer that is free-run, can not stop. Block diagram
is shown in Figure 12-1 .The 8-bit Basic interval timer reg-
ister (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 FF
H
to 00
H
, this
overflow causes to generate the Basic interval timer inter-
rupt. The BITF is interrupt request flag of Basic interval
timer.
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
explained in Power Saving Function. The bit WDTON de-
cides Watchdog Timer or the normal 7-bit timer
Note:
All control bits of Basic interval timer are in CKCTLR
register which is located at same address of BITR
(address EC
H
). Address EC
H
is read as BITR, writ-
ten to CKCTLR. Therefore, the CKCTLR can not be
accessed by bit manipulation instruction.
.
Figure 12-1 Block Diagram of Basic Interval Timer
Figure 12-2 CKCTLR: Clock Control Register
÷
8
÷
16
÷
32
÷
64
÷
128
÷
256
÷
512
÷
1024
0
1
MUX
8
3
fxin
BITR (8BIT)
BITIF
BTS[2:0]
RCWDT
Internal RC OSC
Basic Interval Timer
Interrupt
BTCL
Clear
To Watchdog Timer
Clock Control Register
CKCTLR
ADDRESS : ECH
RESET VALUE : -0010111
Bit Manipulation Not Available
-
WAKEUP
RCWDT
WDTON
BTCL
BTS2
BTS1
BTS0
Basic Interval Timer Clock Selection
000 : fxin
÷
8
001 : fxin
÷
16
010 : fxin
÷
32
011 : fxin
÷
64
100 : fxin
÷
128
101 : fxin
÷
256
110 : fxin
÷
512
111 : fxin
÷
1024
Symbol
Function Description
WAKEUP
1 : Enables Wake-up Timer
0 : Disables Wake-up Timer
RCWDT
1 : Enables Internal RC Watchdog Timer
0 : Disables Internal RC Watchdog Time
WDTON
1 : Enables Watchdog Timer
0 : Operates as a 7-bit Timer
BTCL
1 : BITR is cleared and BTCL becomes “0” automatically
after one machine cycle, and BITR continue to count-up