EM78P568

8-bit OTP Micro-controller

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* This specification are subject to be changed without notice.

21

01/31/2004

V4.7

VII.3 Special Purpose Registers

A (Accumulator)

Internal data transfer, or instruction operand holding

It's not an addressable register.

CONT (Control Register)

7

6

5

4

3

2

1

0

P70EG

INT

TS

RETBK

PAB

PSR2

PSR1

PSR0

Bit 0 ~ Bit 2 (PSR0 ~ PSR2) : TCC/WDT prescaler bits

PSR2

PSR1

PSR0

TCC rate

WDT rate

0

0

0

1:2

1:1

0

0

1

1:4

1:2

0

1

0

1:8

1:4

0

1

1

1:16

1:8

1

0

0

1:32

1:16

1

0

1

1:64

1:32

1

1

0

1:128

1:64

1

1

1

1:256

1:128

Bit 3(PAB) : Prescaler assignment bit

0/1

TCC/WDT

Bit 4(RETBK) : Return value backup control for interrupt routine

0

disable/enable

When this bit is set to 1, the CPU will store ACC,R3 status and R5 PAGE automatically after an interrupt is

triggered. And it will be restored after instruction RETI. When this bit is set to 0, the user need to store ACC,

R3 and R5 PAGE in user program.

Bit 5(TS) : TCC signal source

0

internal instruction cycle clock

1

16.384kHz

Bit 6 (INT) : INT enable flag

0

interrupt masked by DISI or hardware interrupt

1

interrupt enabled by ENI/RETI instructions

Bit 7(P70EG) : interrupt edge type of P70

0

P70 's interruption source is a rising edge signal.

1

P70 's interruption source is a falling edge signal.

CONT register is readable (CONTR) and writable (CONTW).

TCC and WDT :

There is an 8-bit counter available as prescaler for the TCC or WDT. The prescaler is available for the TCC

only or WDT only at the same time.

An 8 bit counter is available for TCC or WDT determined by the status of the bit 3 (PAB) of the CONT

register.

See the prescaler ratio in CONT register.

Fig.17 depicts the circuit diagram of TCC/WDT.

Both TCC and prescaler will be cleared by instructions which write to TCC each time.

The prescaler will be cleared by the WDTC and SLEP instructions, when assigned to WDT mode.

The prescaler will not be cleared by SLEP instructions, when assigned to TCC mode.