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002012-UK 32 channel card
The thing that makes this card different from other DAQ &
Control cards for the PC serial port is the way it communi-
cates with the computer. Many DAQ cards you may have
seen include a microcontroller or a UART chip for serial
communication. The present card does not have any
such chips because it employs direct accessing of UART
registers to enable serial to parallel conversion.
Design by George Vastianos,
Student at Electronics Department, Technological Educational Institute of Piraeus, Greece
32-channel digital
input card for
PC serial port
Main specifications
Number of Inputs: 32
Type of Inputs: TTL compatible
(”0” = 0 V, ”1” = 5 V)
Connection: Serial Port
Communication: Direct access of UART
registers
link your PC to the real world
Power Supply:
9-15 V DC
The field of Data Acquisition (DAQ) &
Control is not something new for
Electronics Science. The field really
started out just after Semiconductor
Technology succeeded in making the
first microprocessor in an Integrated
Circuit (IC) package. These were the
days when computers started to take
a secure position in industry, and after
that, in our homes.
Data Acquisition & Control is all
about processing of data and control-
ling through computers. So the goal of
all DAQ & Control systems is to allow the
computer to communicate with, and to
some extent control, the ‘outside world’.
The applications of DAQ & Control sys-
tems have to do with industry, where
the use of the right input/output cards
enables automation and control sys-
tems to solve complex tasks.
A DAQ & Control Card may have
inputs only, outputs only or a combina-
tion of these. Each input or output may
be analogue or digital. Another char-
acteristic of these cards is the way
they are connected with the comput-
er or computer system. So, many cards
have been designed for installation in
one of the local buses of the main
board (ISA, EISA, PCI etc), or for con-
nection to the available ports of the
computer (parallel, serial, game, key-
board ports).
The project described in this article is a
card with 32 digital inputs (32 Channel
D/I Card) for external connection to
the serial (RS232) port on your IBM PC
or compatible.
INPUTS 24...31
INPUTS 16...23
INPUTS 08...15
INPUTS 00...07
8
8
8
8
BUFFER #4
BUFFER #3
BUFFER #2
BUFFER #1
8
8
8
8
MUX #4
MUX #3
MUX #2
MUX #1
3
3
3
3
About the serial port
1
1
1
1
Serial ports are used mainly for com-
munication between computers, or for
communication between a computer
and peripherals like a modem or a
mouse. The controller at the heart of
this port is almost invariably a UART
(Universal Asynchronous Receiver
Transmitter) chip found on the main
board. This chip works as a serial-to-
parallel and parallel-to-serial adapter.
COM DRIVER / RECEIVER
4
3
COM PORT
002012 - 11
Figure 1. 32-channel D/I card block diagram.
2 - 3/2000 Elektor Electronics EXTRA —————————————— PC T OPICS
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5V
5V
5V
IC1
20
C1
20
C3
IC3
R1
1
8x 10k
74HC541
IC1
IC3
74HC541
R3
1
8x 10k
19
&
10
100n
10
100n
&
19
1
EN
EN
1
K1
23456789
9
8
7
6
5
4
3
2
K2
34
33
2
3
4
18
18
2
3
4
33
34
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
CH16
CH17
CH18
CH19
CH20
CH21
CH22
CH23
32
31
17
17
31
32
30
29
16
16
29
30
28
27
5
6
15
15
5
6
27
28
26
25
14
14
25
26
24
23
7
8
9
13
13
7
8
9
23
24
22
21
12
12
21
22
20
19
11
11
19
20
18
17
17
18
16
15
2
3
4
18
CH8
CH9
CH10
CH11
CH12
CH13
CH14
CH15
CH24
CH25
CH26
CH27
CH28
CH29
CH30
CH31
18
2
3
4
15
16
14
13
17
17
13
14
12
11
16
16
11
12
10
9
5
6
15
15
5
6
9
10
8
7
14
14
7
8
6
5
7
8
9
13
13
7
8
9
5
6
4
3
12
12
3
4
2
1
11
11
1
2
9
8
7
6
5
4
3
2
23456789
5V
1
20
20
&
1
&
EN
C2
C4
19
EN
19
IC2
IC4
R2
1
8x 10k
IC2
10
100n
10
100n
IC4
R4
1
8x 10k
74HC541
74HC541
002012 - 12
5V
5V
Figure 2. Buffers Unit circuit diagram.
A computer may have one to four ser-
ial ports (COM1 to COM4), where
each port occupies eight locations in
its I/O memory area. See Table 1 for
the relevant details.
The basic lines used by a UART in serial
communication for transmission and
reception are called TxD and RxD. Also
a group of extra lines (DCD, DSR, RTS,
CTS, DTR, RI) is used to establish differ-
ent types of serial communication.
Although some of these extra lines
work as inputs and others as outputs,
each one (except RxD) may controlled
through a bit of a UART register. Table 2
summarizes the interface pin connec-
tions and system I/O addresses.
The voltage levels used on the serial
port (RS232 levels) are different from
TTL levels. In RS232 lingo, a logic ‘1’ is
represented by a voltage of –12V, and
a logic ‘0’ by +12V.
Table 1.
Transmit/Receive Buffer
3F8h
2F8h
3E8h
2E8h
Interrupt Enable Register
3F9h
2F9h
3E9h
2E9h
Interrupt Identification Register
3FAh
2FAh
3EAh
2EAh
Line Control Register
3FBh
2FBh
3EBh
2EBh
Modem Control Register
3FCh
2FCh
3ECh
2ECh
Line Status Register
3FDh
2FDh
3EDh
2EDh
Modem Status Register
3FEh
2FEh
3EEh
2Eeh
The hardware
COM Driver/Receiver Unit (where they
are converted from TTL compatible to
RS232 compatible) and arrive at four
serial port inputs (CTS, DSR, RI, DCD). For
the selection of the inputs, we use the
three outputs of on the serial port (TXD,
DTR, RTS). Having passed the COM
Driver/Receiver Unit (and being adapt-
ed from RS232 compatible to TTL com-
patible), the output signals arrive on the
Multiplexers address inputs.
In the block diagram of the circuit
( Figure 1 ), the available inputs have
been divided in four groups of eight
inputs (00-07, 08-15, 16-23, 24-31), and
they all enter the Buffers Unit. After that,
all the lines leaving the Buffers Unit enter
the Multiplexers Unit, where only one
input of each group is selected. The
four selected inputs pass through the
Table 2.
Pin Name
Pin # on
Pin # on
COM1
COM2
COM3
COM4
Bit
I/O
25-pin connector 9-pin connector
TxD
2
3
3FBh
2FBh
3EBh
2EBh
6
O
DTR
20
4
3FCh
2FCh
3ECh
2ECh
0
O
RTS
4
7
3FCh
2FCh
3ECh
2ECh
1
O
CTS
5
8
3FEh
2FEh
3EEh
2EEh
4
I
DSR
6
6
3FEh
2FEh
3EEh
2EEh
5
I
RI
22
9
3FEh
2FEh
3EEh
2EEh
6
I
DCD
8
1
3FEh
2FEh
3EEh
2EEh
7
I
PC T OPICS —————————————— Elektor Electronics EXTRA
3 - 3/2000
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5V
5V
Buffers Unit
In the schematic, Figure 2 , the 32
inputs have been divided in two
groups of 16 (for easy PCB design) and
enter the circuit through connectors K1
and K2. The correspondence between
the inputs and the connectors can be
seen in Table 3 .
All inputs are fitted with pull-up resistors
R1-R4 (10 k
C5
C7
16
100n
100n
16
CH0
4
MUX
5
5
MUX
4
CH16
CH17
CH18
CH19
CH20
CH21
CH22
CH23
0
0
3
2
1
3
2
1
CH1
CH2
CH3
CH4
CH5
CH6
CH7
1
1
6
6
2
IC5
IC7
2
3
74HC151
74HC151
3
15
11
10
11
10
15
4
0
0
4
14
0
7
0
7
14
G
G
5
5
13
9
9
13
) to establish termination
in case where one or more inputs are
not connected. The buffers are the
four chips IC1-IC4 (74HC541). The four
capacitors C1-C4 (100 nF) work as
bypass capacitors to improve the sta-
bility of the circuit. The Output Enable
control inputs (pins 1 and 19) of the
74HC541s are connected to ground
to make the buffers work continuously.
6
2
2
6
12
7
7
12
7
EN
EN
7
8
8
5V
5V
C6
C8
16
100n
100n
16
CH8
CH9
CH10
CH11
CH12
CH13
CH14
CH15
4
MUX
5
5
MUX
4
CH24
CH25
CH26
CH27
CH28
CH29
Multiplexers Unit
As shown in Figure 3 , the multiplexers
are in reality four 74HC151s (IC5-IC8).
Four capacitors C5-C8 (100 nF) are
added to ensure adequate supply
decoupling. The Output Enable con-
trol input (pin 7) of each 74HC151 is
connected to ground to make each
multiplexer work continuously. The A, B,
C address inputs of all 74HC151 are
connected together to implement
multiplexing of all 32 inputs.
0
0
3
2
1
3
2
1
1
1
2
IC6
6
6
IC8
2
3
74HC151
74HC151
3
15
11
10
11
10
15
4
0
0
4
14
0
7
0
7
14
5
G
G
5
13
9
9
13
6
2
2
6
CH30
12
7
7
12
7
EN
EN
7
CH31
8
8
002012 - 13
Figure 3. Multiplexers Unit circuit diagram.
COM Driver/Receiver Unit
The last unit includes a voltage regula-
tor so that the card will not need a reg-
ulated power supply to work. In the
schematic circuit of the COM
Driver/Receiver Unit ( Figure 4 ), IC9
(MAX237) works as an RS232
Driver/Receiver. It has 3 channels con-
verting from RS232 to TTL and 5 chan-
nels converting from TTL to RS232. Five
satellite capacitors (C9-C13; 1
C11
11
C9
10
C1+
V+
9
5V
IC1
K3
12
C1–
D0
D1
D2
D3
7
T1IN
T2IN
T1OUT
T2OUT
2
1
6
3
1
6
F, 35V
max. working voltage) enable the
MAX237 to perform voltage doubling
(so the Driver section can produce a
voltage of 10 V for the five RS232 out-
puts, using a 5 V supply voltage).
Inside the MAX237, each channel has
an inverter. To overcome this problem
we use the four inverted outputs of the
four 74HC151s (pin 6), so that after
inverting two times we have no invert-
ing at all. IC10, a 7805 together with
two capacitors C14 and C15, steps
down the supply voltage to 5 V. Diode
D1 protects the circuit against dam-
age from supply polarity reversal.
µ
18
19
21
2
T3IN
T4IN
T5IN
T3OUT
T4OUT
24
20
7
3
T5OUT
A0
A1
A2
5
R1OUT
R2OUT
R1IN
R2IN
4
8
22
23
4
17
16
9
R3OUT
R3IN
13
C12
5
C10
C2+
MAX237
14
8
C2–
V-
15
C13
C9 ....C13 = 1µ / 35V
LM7805CT
IC10
D1
5V
K4
1N4001
C15
C14
330n
100n
The control software
002012 - 14
The software for the communication
with the card was developed in
QBasic. The communication routine is
called CARD32DI and its source code
Figure 4. COM Driver/Receiver and Power Supply circuit diagram.
4 - 3/2000 Elektor Electronics EXTRA —————————————— PC T OPICS
Ω
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Table 3.
K1
K2
Channel
Pin Number
Channel
Pin Number
00
33
16
33
01
31
17
31
02
29
18
29
03
27
19
27
04
25
20
25
05
23
21
23
06
21
22
21
Figure 5. Screendump of the demo pro-
gram in action.
07
19
23
19
08
15
24
15
09
13
25
13
10
11
26
11
11
9
27
9
may be found in Listing 1 .
If you call this routine (from any program
written in QBasic), follow this syntax:
12
7
28
7
13
5
29
5
14
3
30
3
15
1
31
1
CALL CARD32DI (COMADDRESS,
CHANNEL (), DATA0, DATA1,
DATA2, DATA3)
http://members.xoom.com/
robofreak/download/32dicard.htm
Finally, the author may be reached by
email on sebastian@mail.kapatel.gr
(002012-1)
Where:
COMADDRESS: Integer type variable,
which (before calling) must contain
the base address of the serial port.
Acceptable values of this variable are
&H3F8 (for COM1), &H2F8 (for COM2),
&H3E8 (for COM3), &H2E8 (for COM4).
which for the actual downloading will
take you to the author’s website at
http://www.robofreak.xs3.com
CHANNEL () : Matrix Integer type vari-
able (with pointers from 0 to 31), which
(after calling) contains the logic state
of each channel (values 1 or 0).
REM **************************************
REM * 32 Channel D/I Card *
REM * CARD32DI Communication Routine *
REM * Copyright (c) April 1999 *
REM * by George Vastianos *
REM * email:robofreak@technologist.com *
REM * http://members.xoom.com/robofreak/ *
REM **************************************
‘
SUB CARD32DI (COMADDRESS, CHANNEL(), DATA0, DATA1, DATA2, DATA3)
DATA0, DATA1, DATA2 & DATA3:
Integer type variables that (after call-
ing) contain the arithmetic value of
each group of eight channels (00-07,
08-15, 16-23, and 24-31). The logic
states of all 32 channels make a
Double Word (32 bit) with Ch0 as the LS
Bit and Ch31 as the MS Bit. This Double
Word may be expressed though the
four bytes DATA0, DATA1, DATA2 &
DATA3 where LS Byte is DATA0 and MS
Byte is DATA3. Employ these variables
in cases where you want to save the
logic states of all channels in a file. The
‘compresssion’ allows you to save only
4 bytes instead of a whopping 32.
A demonstration program has been
developed to test the 32-channel D/I
card. A screenshot of this program is
shown in Figure 5 .
To change the serial port address use
the keys <1> to <4>. If you want to
quit, just press <Esc>.
DATA0 = 0: DATA1 = 0: DATA2 = 0: DATA3 = 0
FOR BIT = 0 TO 7
IF (BIT AND 1) = (INP(COMADDRESS + 4) AND 1) THEN
OUT (COMADDRESS + 4), INP(COMADDRESS + 4) XOR 1
END IF
IF (BIT AND 2) = (INP(COMADDRESS + 4) AND 2) THEN
OUT (COMADDRESS + 4), INP(COMADDRESS + 4) XOR 2
END IF
IF (BIT AND 4) = (INP(COMADDRESS + 3) AND 64) / 16 THEN
OUT (COMADDRESS + 3), INP(COMADDRESS + 3) XOR 64
END IF
OUT COMADDRESS + 1, 0
OUT COMADDRESS + 2, 0
INDATA = INP(COMADDRESS + 6) AND 240
CHANNEL(BIT) = (INDATA AND 16) / 16
CHANNEL(BIT + 8) = (INDATA AND 32) / 32
CHANNEL(BIT + 16) = (INDATA AND 64) / 64
CHANNEL(BIT + 24) = (INDATA AND 128) / 128
How to obtain the software
DATA0 = DATA0 + CHANNEL(BIT) * 2 ^ BIT
DATA1 = DATA1 + CHANNEL(BIT + 8) * 2 ^ BIT
DATA2 = DATA2 + CHANNEL(BIT + 16) * 2 ^ BIT
DATA3 = DATA3 + CHANNEL(BIT + 24) * 2 ^ BIT
The source code of the communication
routine (CARD32DI.SUB) and the demon-
stration program (32DICARD.BAS), with
an executable version of the demon-
stration program (32DICARD.EXE) may
be obtained via this website
NEXT BIT
END SUB
PC T OPICS —————————————— Elektor Electronics EXTRA
5 - 3/2000
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