Replacing P/A Comm Circuit Pack - Northern Telecom BCS35 Replacement Manual

104 P/A Comm circuit pack
The P/A Comm pack contains up to eight serial channels; only four are
used. These four are configured as a 1–input, 1–output switch. The input is
connected to the Quad SIO circuit packs in the DPP card racks. The input
interface consists of eight signal lines (plus ground) for each channel. These
lines are connected to a tristatable octal buffer integrated circuit. The
–ASEL signal from the Error Control II circuit pack determines the
input–to–output connection.
The P/A Comm circuit pack may use either internal or external transmit
clocks for all eight channels. Select the clock source by switches S1 and S2,
located as shown in Figure 12–2. Externally transmitted clock signals from
the eight outputs are connected to clock lines on the Quad SIO circuit pack.
See Table 12–1, Table 12–2, and Table 12–3.

Replacing P/A COMM circuit pack

Use the following procedure to replace the P/A Comm circuit pack.
297-1001-536 Standard 01.03 August 1996