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4501

SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

MITSUBISHI ELECTRIC  

MITSUBISHI MICROCOMPUTERS

4501 Group

SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

Table 10 Timer control registers

Timer control register W1

at reset : 00002

at RAM back-up : 00002

R/W

W13 Prescaler control bit

W12 Prescaler dividing ratio selection bit

W11

W10

Timer 1 control bit

Timer 1 count start synchronous circuit

control bit

0

Stop (state initialized)

1

Operating

0

Instruction clock divided by 4

1

Instruction clock divided by 16

0

Stop (state retained)

1

Operating

0

Count start synchronous circuit not selected

1

Count start synchronous circuit selected

W23

W22

W21

W20

Timer control register W2

Timer 2 control bit

Timer 1 count auto-stop circuit selection

bit (Note 2)

Timer 2 count source selection bits

at reset : 00002

at RAM back-up : state retained

0 Stop (state retained)

1 Operating

0 Count auto-stop circuit not selected

1 Count auto-stop circuit selected

W21 W20

Count source

0 0 Timer 1 underflow signal

0 1 Prescaler output (ORCLK)

1 0 CNTR input

1 1 System clock

R/W

Timer control register W6

at reset : 00002

at RAM back-up : state retained

W63 Not used

W62 Not used

W61 CNTR output selection bit

W60 P12/CNTR function selection bit

0

This bit has no function, but read/write is enabled.

1

0

This bit has no function, but read/write is enabled.

1

0

Timer 1 underflow signal divided by 2 output

1

Timer 2 underflow signal divided by 2 output

0

P12(I/O)/CNTR input (Note 3)

1 P12 (input)/CNTR input/output (Note 3)

Notes 1: “R” represents read enabled, and “W” represents write enabled.

2: This function is valid only when the timer 1 count start synchronization circuit is selected.

3: CNTR input is valid only when CNTR input is selected as the timer 2 count source.

R/W

(1) Timer control registers

• Timer control register W1

Register W1 controls the count operation of timer 1, the selection

of count start synchronous circuit, and the frequency dividing ra-

tio and count operation of prescaler. Set the contents of this

register through register A with the TW1A instruction. The TAW1

instruction can be used to transfer the contents of register W1 to

register A.

• Timer control register W2

Register W2 controls the selection of timer 1 count auto-stop cir-

cuit, and the count operation and count source of timer 2. Set the

contents of this register through register A with the TW2A instruc-

tion. The TAW2 instruction can be used to transfer the contents

of register W2 to register A.

• Timer control register W6

Register W6 controls the P12/CNTR pin function and the selec-

tion of CNTR output. Set the contents of this register through

register A with the TW6A instruction. The TAW6 instruction can

be used to transfer the contents of register W6 to register A..

(2) Prescaler

Prescaler is a frequency divider. Its frequency dividing ratio can be

selected. The count source of prescaler is the instruction clock.

Use the bit 2 of register W1 to select the prescaler dividing ratio

and the bit 3 to start and stop its operation. Prescaler is initialized,

and the output signal (ORCLK) stops when the bit 3 of register W1

is cleared to “0.”

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