AD7823

–10–

REV. C

MICROPROCESSOR INTERFACING

The serial interface on the AD7823 allows the parts to be directly

connected to a range of many different microprocessors. This

section explains how to interface the AD7823 with some of the

more common microcontroller serial interface protocols.

AD7823 to PIC16C6x/7x

The PIC16C6x Synchronous Serial Port (SSP) is configured

as an SPI Master with the Clock Polarity Bit = 0. This is done

by writing to the Synchronous Serial Port Control Register

(SSPCON). See PIC16/17 Microcontroller User Manual. Figure

17 shows the hardware connections needed to interface to the

PIC16/PIC17. In this example I/O port RA1 is being used to

pulse

CONVST and enable the serial port of the AD7823.

SCLK

SCK/RC3

SDO/RC5

RA1

AD7823*

PIC16C6x/7x*

CONVST

*ADDITIONAL PINS OMITTED FOR CLARITY

Figure 17. Interfacing to the PIC16/PIC17

AD7823 to MC68HC11

The Serial Peripheral Interface (SPI) on the MC68HC11 is

configured for Master Mode (MSTR = 0), Clock Polarity Bit

(CPOL) = 0, and the Clock Phase Bit (CPHA) = 1. The SPI is

configured by writing to the SPI Control Register (SPCR)—see

68HC11 User Manual. A connection diagram is shown in

Figure 18.

SCLK

SCLK/PD4

MISO/PD2

PA0

AD7823*

MC68HC11*

CONVST

*ADDITIONAL PINS OMITTED FOR CLARITY

Figure 18. Interfacing to the MC68HC11

AD7823 to 8051

The AD7823 requires a clock synchronized to the serial data;

therefore, the 8051 serial interface must be operated in Mode 0.

In this mode serial data enters and exits through RXD, and a serial

clock is output on TXD (half duplex). Figure 19 shows how the

8051 is connected to the AD7823. Here, because the AD7823

shifts data out on the rising edge of the serial clock, the serial

clock must be inverted.

SCLK

TXD

RXD

P1.1

AD7823*

8051*

CONVST

*ADDITIONAL PINS OMITTED FOR CLARITY

Figure 19. Interfacing to the 8051 Serial Port

It is possible to implement a serial interface using the data ports

on the 8051 (or any microcontroller). This would allow direct

interfacing between the AD7823 and 8051 to be implemented

without the need for any “gluing” logic. The technique involves

“bit banging” an I/O port (e.g., P1.0) to generate a serial clock

and using another I/O port (e.g., P1.1) to read in data, see

Figure 20.

SCLK

P1.0

P1.1

P1.2

AD7823*

8051*

CONVST

*ADDITIONAL PINS OMITTED FOR CLARITY

Figure 20. Interfacing to the 8051 Using I/O Ports