Digilent PmodRS232X - Manual (Page 2)

PmodRS232X Reference Manual
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Some older Digilent boards may need a
Digilent Module Interface Board (MIB) and a 6-
pin cable to connect to the PmodRS232X. The
MIB plugs into the system board and the cable
connects the MIB to the PmodRS232X.
(6) Vcc (3.3 - 5V)
(5) GND
(1) CTS
(2) RXD
(3) TXD
(4) RTS
RS232 Module Connector J1
The RS232 module is wired as a DTE device.
RS232 signals are named from the perspective
of the DCE. The TXD signal carries data from
the DCE to the DTE. Therefore, the TXD signal
on pin 3 is connected to the output of a
receiver and should be connected to the
receive input of a UART on the system board.
Similarly, the RXD signal carries data from the
DTE to the DCE and is connected to the input
of a transmitter on the RS232 module and
should be connected to the output of the UART
on the system board.
The CTS signal on pin 1 can be connected to
the input of a transmitter and the RTS signal
on pin 4 can be connected to the output of a
receiver. These connections are made using
jumper blocks JP1 and JP2, as described
below.
Digilent embedded control boards, like the
Cerebot, have one or more connectors with the
UART signals configured correctly for direct
connection of the RS232 module. On Digilent
programmable logic boards like the Basys or
Nexys, a UART must be defined in the logic of
the FPGA or CPLD and the appropriate signal
connections must be defined to connect the
UART to the appropriate connector pins.
Using Jumper Blocks JP1 and JP2
Jumper blocks JP1 and JP2 are used to
configure the RS232 module for either 3-wire
or 5-wire operation. Pins 1 and 2 of JP1 are
connected to pins 1 and 4 of connector J1,
respectively. Pins 1 and 2 of JP2 are
connected to the CTS transmitter and the RTS
receiver, respectively.
To configure the RS232 module as a 3-wire
DTE with no handshaking, place a shorting
block across the two pins of JP2 and ensure
there’s no shorting block on JP1. This loops
RTS back to CTS on the RS232 side of the
module and leaves pins 1 and 4 unconnected
on J1.
To configure the RS232 module as a 5-wire
DTE with RTS/CTS handshaking, place a
shorting block across pin 1 of JP1 and pin 1 of
JP2, and place another shorting block across
pin 2 of JP1 and pin 2 of JP2. This connects
the CTS transmitter to pin 1 of J1 and the RTS
receiver to pin 4 of J1.