HT85F2240 datasheet(102/147 Pages) HOLTEK

102 / 147 page

Rev. 1.10

10� of 147

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A/D Flash 8051 Core Low Pin Count MCU

HT85F2230/HT85F2240

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, P1 and P3 provide

four I/O structure modes option. 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, P1 and P3, 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 SETB 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 P1, A”, while others can operate directly onto

the external port input, such as “MOV A, P1”.

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

Mnemonic

Instruction

Example

Bit Manipulation

ANL

Logica� AND

ANL P�� A

—

ORL

Logica� OR

OR P�� A

—

XRL

Logica� XOR

XRL P�� A

—

�BC

��mp if bit set and then c�ear bit �BC P�.0� (LABEL)

—

CPL

Comp�ement bit

CPL P�.0

—

INC

Increment

INC P�

—

DEC

Decrement

DEC P�

—

D�NZ

Decrement and j�mp if not zero D�NZ P�� (LABEL)

—

MOV Px.�� C

Move carry flag to Bit y of Port x MOV P�.0� C

√

CLR Px.�

C�ear Bit � of Port x

CLR P�.0

√

SETB Px.�

Set Bit � of Port x

SETB P�.0

√

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