SERIES IP521 INDUSTRIAL I/O PACK EIA/TIA-422B SERIAL COMMUNICATION MODULE
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The baud rate is a unit of transmission speed equal to the
number of electrical signals (signal level changes) sent on a line in
one second. It is thus, the electrical signaling rate or frequency at
which electrical impulses are transmitted on a communication line.
The baud rate is commonly confused with the bit transfer rate (bits-
per-second), but baud rate does not equate to the number of bits
transmitted per second unless one bit is sent per electrical signal.
However, one electrical signal (change in signal level) may contain
more than one bit (as is the case with most phone modems). While
bits-per-second (bps) refers to the actual number of bits transmitted
in one second, the baud rate refers to the number of signal level
changes that may occur in one second. Thus, 2400 baud does not
equal 2400 bits per second unless 1 bit is sent per electrical signal.
Likewise, a 1200bps or 2400bps modem operates at a signaling rate
of only 600 baud since they encode 2 and 4 bits, respectively, in one
electrical impulse (through amplitude, phase, and frequency
modulation techniques). However, for this device, the baud rate is
considered equivalent to the bit rate.
Pins 1-40 of the field I/O connector P2 provide connectivity to
serial Ports A-H of this module (Refer to Table 2.1 for pin
assignments). Note that a suffix of ‘_A’, ‘_B’, ‘_C’, to ‘_H’ is
appended to the signal names to indicate their port association. The
receive and transmit signals are described in detail below.
EIA/TIA-422B Signal Descriptions
SIGNAL
DESCRIPTION
RxD_A
RxD_B
to
RxD_H
Receive Data Line (DCE-to-DTE) - This is the receive
data line from the modem to the DTE. The signals on
this line are in serial form. For data to be received the
DTR signal is used to enable the receiver of the port.
TxD_A
TxD_B
to
TxD_H
Transmit Data Line (DTE-to-DCE) - This is the
transmit data line from the DTE to the modem. When
no data is being transmitted, the signal line is held in
the mark state. For data to be transmitted RTS must
all be in the on state (asserted).
An Asterisk (*) is used to indicate an active-low signal.
IP521 OPERATION
Connection to each serial port is provided through connector P2
(refer to Table 2.1). These pins are tied to the inputs and outputs of
EIA/TIA-422B line receivers and drivers. The function of the line
receivers is to convert the required EIA/TIA-422B signals to the TTL
levels required by the UART (Universal Asynchronous
Receiver/Transmitter). The line drivers convert the UART TTL
levels to the EIA/TIA-422B voltage levels. The UART provides the
necessary conversion from serial-to-parallel (receive) and parallel-to-
serial (transmit) for interfacing to the data bus. Additionally, it
provides data buffering and data formatting capabilities. A
programmable logic device is used to control the interface between
the UART and the IP bus.
Note that the field serial interface to the carrier board provided
through connector P2 (refer to Table 2.1) is NON-ISOLATED. This
means that the field signal return and logic common have a direct
electrical connection to each other. As such, care must be taken to
avoid ground loops (see Section 2 for connection
recommendations). Ignoring this effect may cause errors in
operation, and with extreme abuse, possible circuit damage. Refer
to Drawing 4501-714 for example communication wiring
connections.
LOGIC/POWER INTERFACE
The logic interface to the carrier board is made through
connector P1 (refer to Table 2.2). Not all of the IP logic P1 pin
functions are used. P1 also pr5V to power the module.
A programmable logic device installed on the IP Module
provides the control signals required to operate the board. It
decodes the selected addresses in the I/O and ID spaces and
produces the chip selects, control signals, and timing required by
the communication registers, as well as, the acknowledgement
signal required by the carrier board per the IP specification. It also
prioritizes the serving of port interrupts.
5.0 SERVICE AND REPAIR
SERVICE AND REPAIR ASSISTANCE
Surface-Mounted Technology (SMT) boards are generally
difficult to repair. It is highly recommended that a non-functioning
board be returned to Acromag for repair. The board can be easily
damaged unless special SMT repair and service tools are used.
Further, Acromag has automated test equipment that thoroughly
checks the performance of each board. When a board is first
produced and when any repair is made, it is tested, placed in a burn-
in room at elevated temperature, and retested before shipment.
Please refer to Acromag's Service Policy Bulletin or contact
Acromag for complete details on how to obtain parts and repair.
PRELIMINARY SERVICE PROCEDURE
Before beginning repair, be sure that all of the procedures in
Section 2, Preparation For Use, have been followed. Also, refer to
the documentation of your carrier board to verify that it is correctly
configured. Replacement of the module with one that is known to
work correctly is a good technique to isolate a faulty module.
CAUTION: POWER MUST BE TURNED OFF BEFORE
REMOVING OR INSERTING BOARDS
Acromag’s Application Engineers can provide further technical
assistance if required. When needed, complete repair services are
also available from Acromag.
