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B.2.5 Serial Communication
RCM3720 Prototyping Boards sold before 2007 had no RS-232 chip installed, and so no
RS-232 communication was possible. An optional through-hole RS-232 chip could be
installed at U1 or a surface-mount RS-232 chip could be installed at U3. Five correspond-
ing through-hole or surface-mount capacitors must also be installed. Figure B-16 shows
where to install the RS-232 chip and its associated capacitors for the two options.
C13 C10
C12
C13 C10
C12
R6
J5
J2
BT1
RCM3720 PROTOTYPING BOARD
CX1
CX3
CX5
CX7
UX7
RX7
RX8
CX9
RX9
CX10
RX10
UX1
UX8
RX11
RX12
CX11
RX13
CX12
RX14
UX9
RX15
UX2
CX13
RX16
CX14
UX3
Figure B-16. Locations Where to Install RS-232 Chip and Capacitors
NOTE: Only one RS-232 circuit needs to be stuffed.
Rabbit offers the through-hole RS-232 chip and its associated capacitors for sale in a sub-
assembly with some other parts (part number 151-0150). Contact your Rabbit sales repre-
sentative or authorized distributor for more information.
RS-232 serial communication on the RCM3720 Prototyping Board is supported by the
RS-232 transceiver installed at U3. This transceiver provides the voltage output, slew rate,
and input voltage immunity required to meet the RS-232 serial communication protocol.
Basically, the chip translates the Rabbit 3000's signals to RS-232 signal levels. Note that
the polarity is reversed in an RS-232 circuit so that a +5 V output becomes approximately
-10 V and 0 V is output as +10 V. The RS-232 transceiver also provides the proper line
loading for reliable communication.
RabbitCore RCM3700 User's Manual
Surface-Mount Option
• SP232ECT/EET chip
C14
(Z-World part no. 660-0188)
• five 0.1 µF capacitors
U3
(Z-World part no. 321-0004)
C14
U3
U2
J6
C7
C2
C9 D1
C1
J1
J3
J4
PF4
SW1
PB7
SW2
PF6
DS1
PF7
DS2
C5
C8
S3
3
1
C3
2
4
C4
R4
U1
1
3
2
4
R5
C6
1
3
2
4
+5V
GND
DO NOT INSTALL
BOTH OPTIONS!
Through-Hole Option
• SP232ECP chip
(Z-World part no. 660-0006)
• four 0.1 µF capacitors
(Z-World part no. 300-0005)
• one 10 µF capacitor
(Z-World part no. 330-0013)
C 3
C 4
C 5
C 6
0 . 1
C 8
0 . 1
0 . 1
0 . 1
1 0
C5
C8
C3
U1
C4
C6
Header J3
119
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