Hardware Reference
In-Depth Information
are considered logic 0 (the
space
condition). The range of voltages between 23 and 13
V is considered a transition region for which a signal state is not assigned.
3.
Signal transfer distance
.
The signal should be able to transfer correctly within 15 m.
Greater distance can be achieved with good design.
The TIA-232E standard specifies 22 signals. A summary of these signals is given in Table 9.1.
These signals can be divided into six categories.
1.
Signal ground and shield.
2.
Primary communications channel
. This is used for data interchange and includes flow
control signals.
3.
Secondary communications channel
. When implemented, this is used for control of
the remote modem, requests for retransmission when errors occur, and governance
over the setup of the primary channel.
Pin No.
Circuit
Description
1
-
Shield
2
BA
Transmitted data
3
BB
Received data
4
CA/CJ
Request to send/ready for receiving
1
5
CB
Clear to send
6
CC
DCE ready
7
AB
Signal common
8
CF
Received line signal detector
9
-
Reserved for testing
10
-
Reserved for testing
11
-
Unassigned
2
12
SCF/CI
Secondary received line signal detection/data rate selector (DCE source)
3
13
SCB
Secondary clear to send
14
SBA
Secondary transmitted data
15
DB
Transmitter signal element timing (DCE source)
16
SBB
Secondary received data
17
DD
Receiver signal element timing
18
LL
Local loopback
19
SCA
Secondary request to send
20
CD
DTE ready
21
RL/CG
Remote loopback/signal quality detector
22
CE
Ring indicator
Data signal rate selector (DTE/DCE source)
3
23
CH/CI
24
DA
Transmitter signal element timing (DTE source)
25
TM
Test mode
1. When hardware fl ow control is required, circuit CA may take on the functionality of circuit CJ. This is one
change from the former TIA-232.
2. Pin 11 is unassigned. It will not be assigned in future versions of TIA-232. However, in international standard ISO
2110, this pin is assigned to select transmit frequency.
3. For designs using interchange circuit SCF, interchange circuits CH and CI are assigned to pin 23. If SCF is
not used, CI is assigned to pin 12.
Table 9.1
■
Functions of EIA-232E signals
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