Owner's manual

Application Hints (Continued)

TL/H/12079–46

Note: V

, and V

REF

on the ADC12138 each have 0.01 mF and 0.1 mF chip caps, and 10 mF tantalum caps. All logic devices are bypassed with 0.1 mF

caps.

The assignment of the RS232 port is shown below

B7 B6 B5 B4 B3 B2 B1 B0

COM1

Input Address 3FE X X X CTS X X X X

Output Address 3FC X X X 0 X X RTS DTR

A sample program, written in Microsoft QuickBasic, is

shown on the next page. The program prompts for data

mode select instruction to be sent to the A/D. This can be

found from the Mode Programming table shown earlier. The

data should be entered in ‘‘1’’s and ‘‘0’’s as shown in the

table with DI0 first. Next the program prompts for the num-

ber of SCLKs required for the programmed mode select in-

struction. For instance, to send all ‘‘0’’s to the A/D, selects

CH0 as the

input, CH1 as the

input, 12-bit conversion,

and 13-bit MSB first data output format (if the sign bit was

not turned off by a previous instruction). This would require

13 SCLK periods since the output data format is 13 bits. The

part powers up with No Auto Cal, No Auto Zero, 10 CCLK

Acquisition Time, 12-bit conversion, data out with sign, pow-

er up, 12- or 13-bit MSB First, and user mode. Auto Cal,

Auto Zero, Power Up and Power Down instructions do not

change these default settings. Since there is no CS

signal to

synchronize the serial interface the following power up se-

quence should be followed:

1. Run the program

2. Prior to responding to the prompt apply the power to the

ADC12138

3. Respond to the program prompts

It is recommended that the first instruction issued to the

ADC12138 be Auto Cal (see Section 1.1).