VULCAN Technical Manual
Detailed hardware description
© 2007 Eurotech Ltd Issue D
33
COM3 – RS232 interface
Supported on channel A of an external XR162551L UART. The port is buffered to
RS232 levels by a 3V transceiver with ±15kV ESD protection, and supports full
handshaking and modem control signals. The maximum baud rate on this channel is
115.2KBaud. A factory fit option configures COM2 as a TTL, so that it can be interfaced
directly to an embedded modem. Please contact Eurotech for details. See
.
COM4 – RS422/485 interface
Supported on channel B of an external XR162551L UART, and buffered to RS422/485
levels by a 5V transceiver with ±15kV ESD protection, to provide support for RS422
(default) and RS485 (jumper selectable) interfaces. The maximum baud rate on this
channel is 115.2KBaud.
This channel can be configured as either RS422 or RS485. Further details about these
interfaces are provided below:
•
RS422
The RS422 interface provides full-duplex communication. The signals available are
TX+, TX-, RX+, RX- and ground. The maximum cable length for an RS422 system
is 4000ft (1200m). It supports one transmitter and up to ten receivers.
To enable RS422 operation, jumpers must be fitted in positions A2-A1 & B2-B1 on
the JP1 jumper header. Jumpers in positions A4-B4 & A5-B5 must be fitted if the
board is at the end of the network. See
, page
, for details.
•
RS485
This is a half-duplex interface that provides combined TX and RX signals.
Connector J7 pin 5 provides TX+/RX+ and pin 6 provides TX-/RX-. A ground
connection is also required for this interface. The maximum cable length for this
interface is the same as RS422 (4000ft), but RS485 supports up to 32 transmitters
and receivers on a single network. Only one transmitter should be switched on at a
time. The VULCAN uses the RTS signal to control transmission. When this signal is
at logic 1 the driver is switched off and data can be received from other devices.
When the RTS line is at logic 0 the driver is on. Any data transmitted from the
VULCAN is automatically echoed back to the receiver. This enables the serial
communications software to recognise that all data has been sent and disable the
transmitter when required.
Jumpers must be fitted in positions A2-A3 & B2-B3 to enable the RS485 interface.
Jumpers in positions A4-B4 & A5-B5 provide parallel line termination 120 Ohm
resistors and must be fitted if the VULCAN is at the end of the network.
The UART used on the VULCAN for COM4 has extended features including auto-
RTS control for RS485. This forces the RTS signal to change state (and therefore
the direction of the RS485 transceivers) when the last bit of a character has been
sent onto the wire. Please refer to the XR162551L datasheet, which is on the
accompanying Development Kit CD.