SERIES IOS-521 I/O SERVER MODULE EIA/TIA-422B SERIAL COMMUNICATION MODULE
__________________________________________________________________________________________
- 17 -
a break signal is longer than one character time. That is, it is any
“space” condition on the line that lasts longer than a single
character (including its framing bits) and is usually 1-1/2 to 2
character times long.
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.
IOS-521 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 IOS 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 RS422/RS485 INTERFACE DIAGRAM for
example communication wiring connections.
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.
