HT85F2270 datasheet(126/226 Pages) HOLTEK

126 / 226 page

Rev. 1.00

1�6 of ��6

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Standard 8051 8-Bit Flash MCU

HT85F2260/HT85F2270/HT85F2280

Programming Considerations

Within the user program, one of the first things to consider is port initialisation. After a reset, the

I/O data register will be set high and I/O port mode registers will be cleared to low. This means that

all I/O pins will default to a Quasi-bidirectional structure. The I/O pins can be re-assigned to some

other mode for each I/O using the control registers, PnM0 and PnM1. Ports P0~P3 provide four I/O

structure modes option while the P4 and P5 only provide a Quasi-bidirectional I/O structure mode.

Care should be taken to setup the correct I/O structure for each I/O pin, otherwise unexpected data

will be input or output on the I/O pins.

The data registers, P0~P5, reflect the value of the corresponding I/O port, however, they do not

necessarily reflect the I/O pin logic state. During reading and writing of data to these registers,

what actually happens is dependent upon whether the corresponding pin is setup as an output or

input. A write operation is only effective when the corresponding pin is setup as an output. In such

cases a write operation will setup the logic level, low or high, on the pin. A read operation will read

the current logic level, low or high, on the corresponding pin.

If any pins are setup to be used as A/D input pins then it is important to ensure that the I/O Port

Mode registers setup the pins as inputs, which are essentially high impedance inputs. In this way

the I/O logic circuits will have a minimal influence on the A/D input impedance.

When using these bit control instructions, a read-modify-write operation takes place. The

microcontroller must first read in the data on the entire port, modify it to the required new bit

values and then rewrite this data back to the output ports, such as using CLR or SET bit write

instructions. Care should be taken that some instructions, the Read-Modify-Write instructions,

operate on the Pn register, such as “INC P0” or “ANL P2, A”, while others can operate directly

onto the external port input, such as “MOV A, P1”. Note that P4 and P5 cannot be modified by

bit manipulation instructions as their registers are not located in bit addressable space. In case of

reading, the state of P4 and P5 registers reflects the value of the corresponding I/O port.

The accompanying table illustrates the Read-Modify-Write related instructions.

Mnemonic

Instruction

Example

Bit Manipulation

ANL

Logical AND

ANL P�� A

—

ORL

Logical OR

OR P�� A

—

XRL

Logical XOR

XRL P�� A

—

JBC

Jump if bit set and then clear bit

JBC P�.0� (LABEL)

—

CPL

Complement bit

CPL P�.0

—

INC

Increment

INC P�

—

DEC

Decrement

DEC P�

—

DJNZ

Decrement and jump if not zero

DJNZ P�� (LABEL)

—

�OV Px.�� C

Move carry flag to Bit y of Port x

�OV P�.0� C

CLR Px.�

Clear Bit � of Port x

CLR P�.0

SET Px.�

Set Bit � of Port x

SET P�.0

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