T W R - 9 S 1 2 G 1 2 8
J U N E 2 , 2 0 1 0
U S E R G U I D E
10
TIMING
The TWR-S12G128 internal timing source is active from RESET by default. An external 8MHz
crystal oscillator, configured for low-power operation, is also installed. Refer to the target
device RM for details on selecting and configuring the desired timing source.
COMMUNICATIONS
Communications options for the TWR-S12G128 include serial RS-232, LIN, and CAN. Serial
RS-232 communications is supported through a RS-232 physical layer device (PHY) and a 2x5
pin header. A high-speed, enhanced, LIN PHY provides LIN bus communications through a
2x2 Molex connector (pn 39-29-1048). A high-speed CAN PHY provides CAN bus
communications through a 1 x 4 Molex connector (pn 39-30-3045).
Connecting LIN cables require Molex housing, pn 39-01-2040 and pins, pn 39-00-0217.
Connecting CAN cables require Molex housing, pn 39-01-4040, and pins, pn 39-00-0217.
The COM_SEL option header connects the MCU SCI signal to either the LIN PHY or the RS-
232 PHY. See Figure 6 below for jumper position options. See Figure 4 below for jumper
position options.
RS-232
The TWR-S12G128 applies the MAX3387E, RS-232 transceiver to support serial
communications.
A standard 2x5 “Berg” pin-header on 0.1” centers and an IDC to DB9 cable
supports connecting standard serial cables to the target board. Figure 4 below shows the SCI
signal connections.
Figure 4: Serial Connections
MCU Port Signal
Transceiver
Signal
COM
CONNECTOR
COMMENTS
+5V
J5-1
PS1//TXD0
TXD
J5-3
pull-up
PS0//RXD0
RXD
J5-5
PAD9/KWAD9/AN9
DTR
J5-7
CT2 (NC)
GND
J5-9
PD2
DSR
J5-2
pull-up
PD1
CTS
J5-4
CT3 (NC), pull-up
PAD10/KWAD10/AN10
RTS
J5-6
pull-up
TP2
J5-8
PAD8/KWAD8/AN8
INVALID*
CT4 (NO)
PAD15/KWAD15/AN15
FORCEOFF*
CT5 (NC)
NOTE:
For normal RS-232 operation, FORCEOFF* should be actively driven to the high level.
Alternately, open CT5 to allow FORCEOFF* to float high.
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