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AS1504, AS1505

Data Sheet

Microprocessor Interfaces

Microprocessor Interfaces

The AS1504/AS1505 serial interface provides a simple connection to a wide range of microprocessors, most of which

have built-in serial data capability that can be used for communicating with the device.

Note:

In cases where a serial port is not available on the microprocessor, the AS1504/AS1505 can be addressed via

software.

Eleven data bits are required to load data into the AS1504/AS1505 (3 bits for the DAC address and 8 bits for the DAC

value). If more than eleven bits are transmitted before the microprocessor chip select input goes high, the most-signifi-

cant bits are ignored. Because most microprocessors transmit data in 8-bit words, it will need to send 16 bits to the

AS1504/AS1505; however, the AS1504/AS1505 only responds to the last 11 bits clocked into the SDI input, so the

serial data interface is not affected.

8051 Microprocessor Interface

Figure 22 shows the AS1504/AS1505 interface to an 8051 microprocessor. This interface uses the 8051 internal serial

port as a simple 8-bit shift register (Mode 0 operation). 8051 Port3.0 serves as the serial data output port and Port3.1

serves as the serial clock.

Figure 22. AS1504-to-8051 Microprocessor Interface

cally converted to serial format and clocked out via Port3.0 and Port3.1. Once 8 bits have been transmitted, the trans-

mit interrupt flag (SCON.1) is set and the next 8 bits can be transmitted.

The AS1504/AS1505 requires that CSN goes low at the start of the serial data transfer. Additionally, pin CLK must be

high when CSN goes high at the end of each data transfer. The 8051 serial clock meets these requirements, since

Port3.1 begins and ends the serial data transfer in a high state.

AS1504

OUT8

OUT1

SDI

CLK

RSN

SHDNN

CSN

8051

Port3.0

Port3.1

Port1.3

Port1.2

Port1.1

RX

TX

Serial Data

Shift Register

Shift Clock

1.1

1.2

1.3

Port 1

0.1µF

10µF

Tantalum

+

+5V