ADC12138CIWM datasheet(36/41 Pages) NSC

36 / 41 page

Application Hints (Continued)

The assignment of the RS232 port is shown below

COM1

Input Address

3FE

CTS

Output Address

3FC

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 number of SCLKs required

for the programmed mode select instruction. 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 out-

put format (if the sign bit was not turned off by a previous in-

struction). This would require 13 SCLK periods since the out-

put data format is 13 bits. The part powers up with No Auto

Cal, No Auto Zero, 10 CCLK Acquisition Time, 12-bit conver-

sion, data out with sign, power 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 inter-

face the following power up sequence should be followed:

Run the program

Prior to responding to the prompt apply the power to the

ADC12138

Respond to the program prompts

It is recommended that the first instruction issued to the

ADC12138 be Auto Cal (see Section 1.1).

Code Listing:

’variables DOL=Data Out word length, DI=Data string for A/D DI input,

’

DO=A/D result string

’SET CS# HIGH

OUT <&amp>H3FC, (<&amp>H2 OR INP (<&amp>H3FC)

’set RTS

HIGH

OUT <&amp>H3FC, (<&amp>HFE AND INP(<&amp>H3FC)

’SET DTR LOW

OUT <&amp>H3FC, (<&amp>HFD AND INP (<&amp>H3FC)

’SET RTS LOW

OUT <&amp>H3FC, (<&amp>HEF AND INP(<&amp>H3FC))

’set B4 low

LINE INPUT <&ldquo>DI data for ADC12138 (see Mode Table on data sheet)<&rdquo>; DI$

INPUT <&ldquo>ADC12138 output word length (12,13,16 or 17)<&rdquo>; DOL

’SET CS# HIGH

OUT <&amp>H3FC, (<&amp>H2 OR INP (<&amp>H3FC)

’set RTS

HIGH

OUT <&amp>H3FC, (<&amp>HFE AND INP(<&amp>H3FC)

’SET DTR LOW

OUT <&amp>H3FC, (<&amp>HFD AND INP (<&amp>H3FC)

’SET RTS LOW

DS012079-46

Note: VA

+,V

+, and V

REF

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

caps.

ADC12138CIWM Datasheet(PDF) 36 Page - National Semiconductor (TI)

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