Design of serial interface between AD7543 and 89C2051

Design of serial interface between AD7543 and 89C2051

This paper introduces the method of realizing serial interface through the P1 port of 89C2051 with 12-bit serial input digital-to-analog converter AD7543.
Keywords: D/A converter, microcontroller, serial interface

1 Introduction
AD7543 is a 12-bit CMOS single-chip serial input digital-to-analog converter (DAC) produced by AD Company of the United States. It is a precision multiplication DAC designed for serial interface. Its digital data is input one bit at a time from high to low. The main characteristics and technical indicators of AD7543:

Resolution 12 bits

Non-linearity error ±1/2LSB

Input method Serial

Serial Load Positive or Negative Strobe

Initialization Asynchronous Clear Input

Working voltage: +5V

Maximum power consumption 400mW

The on-chip logic circuit of AD7543 consists of a 12-bit serial input parallel output shift register (register A) and a 12-bit DAC input register (register B). The data appearing on the SRI pin of AD7543 is loaded into register A at a fixed time when the rising edge of the select input signal STB1, STB2 or STB4 or the falling edge of STB3 (selected by the user). Once register A is full, the data of register A is loaded into register B under the control of the load pulse.

2 Interface mode
89C2051 is a high-performance single-chip microcomputer, which is highly compatible with the MCS51 series instructions. Since there is no dedicated serial data interface, the interface with AD7543 can only be realized through programmable I/O pins and corresponding software. As shown in Figure 1, P1.0 is the serial data output port, which is connected to SRI of AD5743; STB1, one of the four control input terminals of register A inside AD7543, is connected to P1.1 as a pulse for receiving data, STB2 and STB4 are grounded, and STB3 is connected to +5V; the clear input CLR of register B of AD7543 is connected to P1.3; the two control load input terminals LD1 and LD2 of register B are grounded and connected to P1.2 respectively. After the hardware circuit connection is completed, the remaining is software work.

The rich instruction system of the 51 series brings great convenience to the D/A conversion of serial input. Assuming that the 12-bit data is placed in the R2 and R3 registers of the single-chip microcomputer, the serial data transmission can be realized by operating the accumulator A, carry flag and P1 port of the single-chip microcomputer. The following is a list of D/A conversion subroutines:

STATR: CLR P1.3

CLR P1.3

SETB P1.2

CLR C

CLR A

MOVA, R2

MOV R7, #4

LOOP1: PLC A

DJNE R7, LOOP1

MOV R7, #4

LOOP2: LCALL PRD

DJNE R7, LOOP2

CLR C

CLR A

MOV A，R3

MOV R7, #8

LOOP3: LCALL PRD

DJNE R7, LOOP3

CPL P1.2 loads data and starts conversion

RET

Read data subroutine:

PRD: RLC A

MOV P1.0, C

SETB P1．1

CPL P1.1

RET
The program given above can be used as a subroutine to call the serial interface between the AD7543 converter and the 51 series microcontroller.
3 Conclusion
This interface method makes full use of the software and hardware resources of the microcontroller itself and simplifies the circuit design. However, because the data is read in one by one and is also related to the number of data bits of the converter, this interface method is only suitable for occasions where time requirements are not high.