ADC12030CIWM National Semiconductor, ADC12030CIWM Datasheet - Page 37

• Manufacturer Part Number: ADC12030CIWM
• Description: Self-Calibrating 12-Bit Plus Sign Serial I/O A/D Converters with MUX and Sample/Hold
• Manufacturer: National Semiconductor

Application Hints
15.0 AN RS232 SERIAL INTERFACE
Shown on the following page is a schematic for an RS232 in-
terface to any IBM and compatible PCs. The DTR, RTS, and
CTS RS232 signal lines are buffered via level translators
Note: V
caps.
The assignment of the RS232 port is shown below
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. The
following power up sequence should be followed:
1. Run the program
2. Prior to responding to the prompt apply the power to the
3. Respond to the program prompts
It is recommended that the first instruction issued to the
ADC12038 be Auto Cal (see Section 1.1).
ADC12038
A
+
, V
D
+
, and V
REF
COM1
+
on the ADC12038 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
Input Address
Output Address
(Continued)
3FE
3FC
B7
X
X
B6
37
X
X
and connected to the ADC12038’s DI, SCLK, and DO pins,
respectively. The D flip flop drives the CS control line.
B5
X
X
CTS
B4
0
B3
X
X
B2
X
X
RTS
B1
X
DS011354-44
DTR
B0
X
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