IBM 3270 Manual page 245

Modem Address Switches (Integrated Modems with
Speeds Greater Than 1200 BPS Only)
H-8
The Modem Address switches are installed only on a 3274 Model 51C that
has an integrated modem feature. (#5640, 57 40, 5840, or 5842) installed.
These switches are located behind a door on the control panel. These
switches must be set to the binary equivalent of either your BSC control
unit address (this is the hexadecimal polling address you obtained from the
system programmer for your response to sequence number 301) or your
SDLC control unit address (this is your response to sequence number 302).
Failure to set the Modem Address switches properly will result in valid data
operations of the 3274 but inability to execute the link problem
determination aid (LPDA) function of the integrated modem.
Use Figure H-3 to convert your sequence number response to its binary
equivalent. For example, if your response to sequence number 301 is 21, the
eight Modem Address switches should be set as shown in Figure H-4.
Enter the Modem Address switch settings in Step 2 of the instructions
following Figure H-4. Give the completed instructions to the person who
will customize the 327 4.
Numeric Modem Address Switch
Value Settings
0
Off
Off
Off
Off
1 Off Off Off On
2 Off
Off On Off
3 Off Off On On
4 Off On Off Off
5 Off On Off On
6 Off On On Off
7 Off On On On
8
On
Off
Off
Off
9
On Off Off On
A On Off On Off
B On Off On On
c
On On Off Off
D
On On Off On
E On On On Off
F
On On On On
Figure H-3. Conversion of BSC Control Unit Address and SDLC Control
Unit Address to Binary-Equivalent Modem Address Switch
Settings on 3274 Model 51C
Response to
Sequence Number 301 2 1
Switch Number 1
2
3
4
5 6
7 8
Switch Setting Off
Off
On
Off Off Off Off On
Figure H-4. Example of 3274 Model 51C Modem Address Switch Settings