Application hints – Rainbow Electronics ADC12L038 User Manual
Page 33
Application Hints
(Continued)
15 0 AN RS232 SERIAL INTERFACE
Shown below is a schematic for an RS232 interface to any
IBM and compatible PCs The DTR RTS and CTS RS232
signal lines are buffered via level translators and connected
to the ADC12L038’s DI SCLK and DO pins respectively
The D flip flop drive the CS control line
TL H 11830 – 45
Note
V
A
a
V
D
a
and V
REF
a
on the ADC12L038 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 DS14C335 has an internal DC-DC converter that generates the necessary TIA EIA-232-E output levels from a 3 3V supply There are four 0 47 mF
capacitors required for the DC-DC converter that are not shown in the above schematic
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
TM
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 ainput CH1 as the binput 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 12- or 13-bit MSB First power up and user mode
Auto Cal Auto Zero Power UP and Power Down instruc-
tions 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
ADC12L038
3 Respond to the program prompts
It is recommended that the first instruction issued to the
ADC12L038 be Auto Cal (see Section 1 1)
33