HT46R46E datasheet(10/45 Pages) HOLTEK

10 / 45 page

HT46R46E/HT46C46E

Rev. 1.30

July 19, 2005

The ALU not only saves the results of a data operation but

also changes the status register.

Status Register

- STATUS

This 8-bit register (0AH) contains the zero flag (Z), carry

flag (C), auxiliary carry flag (AC), overflow flag (OV),

power down flag (PDF), and watchdog time-out flag

(TO). It also records the status information and controls

the operation sequence.

With the exception of the TO and PDF flags, bits in

the status register can be altered by instructions like

most other registers. Any data written into the status

tion operations related to the status register may give

different results from those intended. The TO flag

can be affected only by system power-up, a WDT

time-out or executing the

²CLR WDT² or ²HALT² in-

struction. The PDF flag can be affected only by exe-

cuting the

²HALT² or ²CLR WDT² instruction or a

system power-up.

The Z, OV, AC and C flags generally reflect the status of

the latest operations.

In addition, on entering the interrupt sequence or exe-

cuting the subroutine call, the status register will not be

pushed onto the stack automatically. If the contents of

the status are important and if the subroutine can cor-

rupt the status register, precautions must be taken to

save it properly.

Interrupt

The device provides an external interrupt, internal

timer/event counter interrupt and A/D converter inter-

rupts. The Interrupt Control Register (INTC;0BH) con-

tains the interrupt control bits to set the enable or disable

and the interrupt request flags.

Once an interrupt subroutine is serviced, all the other in-

terrupts will be blocked (by clearing the EMI bit). This

scheme may prevent any further interrupt nesting. Other

interrupt requests may happen during this interval but

only the interrupt request flag is recorded. If a certain in-

terrupt requires servicing within the service routine, the

EMI bit and the corresponding bit of INTC may be set to

allow interrupt nesting. If the stack is full, the interrupt re-

quest will not be acknowledged, even if the related inter-

rupt is enabled, until the SP is decremented. If immediate

service is desired, the stack must be prevented from be-

coming full.

All these kinds of interrupts have a wake-up capability.

As an interrupt is serviced, a control transfer occurs by

pushing the program counter onto the stack, followed by

a branch to a subroutine at specified location in the pro-

gram memory. Only the program counter is pushed onto

the stack. If the contents of the register or status register

(STATUS) are altered by the interrupt service program

which corrupts the desired control sequence, the con-

tents should be saved in advance.

External interrupts are triggered by a high to low transi-

tion of INT and the related interrupt request flag (EIF; bit

4 of INTC) will be set. When the interrupt is enabled, the

stack is not full and the external interrupt is active, a sub-

routine call to location 04H will occur. The interrupt re-

quest flag (EIF) and EMI bits will be cleared to disable

other interrupts.

The internal timer/event counter interrupt is initialized by

setting the timer/event counter interrupt request flag

(TF;bit 5 of INTC), caused by a timer overflow. When the

interrupt is enabled, the stack is not full and the TF bit is

set, a subroutine call to location 08H will occur. The re-

lated interrupt request flag (TF) will be reset and the EMI

bit cleared to disable further interrupts.

Bit No.

Label

Function

C is set if the operation results in a carry during an addition operation or if a borrow does not take

place during a subtraction operation; otherwise C is cleared. C is also affected by a rotate

through carry instruction.

1AC

AC is set if the operation results in a carry out of the low nibbles in addition or no borrow from the

high nibble into the low nibble in subtraction; otherwise AC is cleared.

Z is set if the result of an arithmetic or logic operation is zero; otherwise Z is cleared.

3OV

OV is set if the operation results in a carry into the highest-order bit but not a carry out of the high-

est-order bit, or vice versa; otherwise OV is cleared.

PDF

PDF is cleared by system power-up or executing the

²CLR WDT² instruction. PDF is set by exe-

cuting the

²HALT² instruction.

5TO

TO is cleared by system power-up or executing the

²CLR WDT² or ²HALT² instruction. TO is set

by a WDT time-out.

6, 7

Unused bit, read as

²0²

Status (0AH) Register

HT46R46E Datasheet(PDF) 10 Page - Holtek Semiconductor Inc

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