IBM 3872 User Manual page 36

mitted data' line. The 3872 raises (turns on) and drops
(turns off) this timing line at the selected bits-per-second
rate, whenever it is plugged in and turned on.
• 'Received data' - The receiving modem controls this line
to present data to the DTE.
• 'Receive signal element timing' - The receiving modem
drops (turns off) this line at the optimum time, when the
DTE should sample each bit on the 'received data' line.
The bit may be of the same binary value (on or 1 ; off or 0)
as the previous bit, or it may be of the opposite value.
The 3872 Modem raises (turns on) and
~:lrops
(turns off)
this timing line at the selected bits-per-second rate, when-
ever it is plugged in and turned on.
• 'Data set ready' - When the modem is operable, it raises
(turns on) this line to the DTE. With the 3872, modem
power must be on, and the modem must not be in local
test (see "Modem Test Concepts," in Part I). In addition
...._
---
:.....
-
...._
--
...._
---
[
DTE controls these lines
Common lines
r
f
3872 oootcol• th .. ,
n ""
Transmitted Data
Transmit Signal Element Timing
Received Data
Receive Signal Element Timing
Data Set Ready
Request to Send
in a switched network operation, 'data set ready' indicates
a connection to the switched network channel. 'Data set
ready' remains on as long as these conditions are met.
• 'Request to send' - The DTE raises (turns on) this line
when it wishes to send. 'Data set ready' must be on, and
for proper operation, it is necessary that 'clear to send
(ready for sending)' be off. When the DTE turns on
'request to send', the IBM 3872 Modem configured for
half-duplex operation (Figure 1-5) holds 'data carrier
detected' and 'received data' off. This action is known
as "clamping". 'Request to send' must be turned off
when the DTE has finished sending.
•'Clear to send (ready for sending)' - After a suitable time
interval, known as a "delay", the modem raises (turns on)
this line
ill
response to 'request to send'. In half-duplex
operation, the delay is needed to perform the clamping,
start generating carrier, and allow time for the receiving
IBM 3872 Modem
.....
r '
(free-running)
(may be clamped off)
(free-running)
(power on and not test)
(always on in some configurations)
__.,
,...
...._
Clear to Send (Ready for Sending) (may be delayed)
--
Data Carrier Detected (Received Line Signal Detector)
...._
DTE
--
(Data Terminal Equipment)
Data Signal Rate Selector
*New Sync
**Test
Protective Ground
--
---
...._
Signal Ground
-
Ring Indicator (Calling Indicator)
--
-
Data Terminal Ready
***(Select Standby)
h T
n t•
h w
(T e CCIT des1g a ion 1s s o n
in
parentheses 1f 1t differs
from the EIA Standard.)
* New Sync is not standardized by EIA or CCITT.
** Test is not standardized by CCITT.
*** Select Standby is not standardized by EIA.
.
--
.....
~
.....
~
. .
_.,
--
_... --
......
r"
(may be clamped off)
(also switch-control led)
(resets synchronization)
(also switch-control led)
(often prohibited)
(a I ways connected)
(automatic answer)
(allow automatic answer)
(also switch-controlled)
Note l: DTE interface lines not controlled by an originating machine are interpreted by the other machine to be down or off (standard).
Note 2: DTE interface standards can be obtained from the sources given in the notice "To The Reader", at the front of this manual.
Figure 3-1. Modem-DTE Interface
3-2 IBM 3872 Modem User's Guide
~
Line