HT48R064 datasheet(21/93 Pages) HOLTEK

21 / 93 page

HT48R063/064/065/066/0662/067

Rev. 1.10

June 9, 2009

Memory will always result in Bank 0 being accessed irre-

spective of the value of the Bank Pointer.

Status Register

- STATUS

This 8-bit register 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).

These arithmetic/logical operation and system manage-

ment flags are used to record the status and operation of

the microcontroller.

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 register

will not change the TO or PDF flag. In addition, opera-

tions related to the status register may give different re-

sults due to the different instruction operations. The TO

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

time-out or by executing the

²CLR WDT² or ²HALT² in-

struction. The PDF flag is affected only by executing the

²HALT² or ²CLR WDT² instruction or during a system

power-up.

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

the latest operations.

In addition, on entering an interrupt sequence or execut-

ing a subroutine call, the status register will not be

pushed onto the stack automatically. If the contents of

the status registers are important and if the interrupt rou-

tine can change the status register, precautions must be

taken to correctly save it. Note that bits 0~3 of the

STATUS register are both readable and writeable bits.

Input/Output Ports and Control Registers

Within the area of Special Function Registers, the port

PA, PB, etc data I/O registers and their associated con-

trol register PAC, PBC, etc play a prominent role. These

registers are mapped to specific addresses within the

Data Memory as shown in the Data Memory table. The

data I/O registers, are used to transfer the appropriate

output or input data on the port. The control registers

specifies which pins of the port are set as inputs and

which are set as outputs. To setup a pin as an input, the

corresponding bit of the control register must be set

high, for an output it must be set low. During program in-

itialisation, it is important to first setup the control regis-

ters to specify which pins are outputs and which are

inputs before reading data from or writing data to the I/O

ports. One flexible feature of these registers is the ability

to directly program single bits using the

²SET [m].i² and

²CLR [m].i² instructions. The ability to change I/O pins

from output to input and vice versa by manipulating spe-

cific bits of the I/O control registers during normal pro-

gram operation is a useful feature of these devices.

· STATUS Register

Bit

76543210

Name

¾¾

PDF

R/W

¾¾

R/W

POR

¾¾

xxxx

²x² unknown

Bit 7, 6

Unimplemented, read as

²0²

Bit 5

TO: Watchdog Time-Out flag

0: After power up or executing the

²CLR WDT² or ²HALT² instruction

1: A watchdog time-out occurred.

Bit 4

PDF: Power down flag

0: After power up or executing the

²CLR WDT² instruction

1: By executing the

²HALT² instruction

Bit 3

OV: Overflow flag

0: no overflow

1: an operation results in a carry into the highest-order bit but not a carry out of the

highest-order bit or vice versa.

Bit 2

Z: Zero flag

0: The result of an arithmetic or logical operation is not zero

1: The result of an arithmetic or logical operation is zero

Bit 1

AC: Auxiliary flag

0: no auxiliary carry

1: an 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

Bit 0

C: Carry flag

0: no carry-out

1: an operation results in a carry during an addition operation or if a borrow does not take place

during a subtraction operation

C is also affected by a rotate through carry instruction.

HT48R064 Datasheet(PDF) 21 Page - Holtek Semiconductor Inc

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