
Communications Processor (CP)
MOTOROLA
MC68302 USER’S MANUAL
4-11
4.4.1 IDL Interface
The IDL interface is a full-duplex ISDN interface used to interconnect a physical layer device
(such as the Motorola ISDN S/T transceiver MC145474) to the integrated multiprotocol pro-
cessor (IMP). Data on five channels (B1, B2, D, A, and M) is transferred in a 20-bit frame
every 125
μ
s, providing 160-kbps full-duplex bandwidth. The IMP is an IDL slave device that
is clocked by the IDL bus master (physical layer device). The IMP provides direct connec-
tions to the MC145474. Refer to Figure 4-6 for the IDL bus signals.
The IMP supports 10-bit IDL as shown in Figure 4-6; it does not support 8-bit IDL.
Figure 4-6. IDL Bus Signals
An application of the IDL interface is to build a basic rate ISDN terminal adaptor (see Figure
4-7). In such an application, the IDL interface is used to connect the 2B + D channels be-
tween the IMP, CODEC, and S/T transceiver. One of the IMP SCCs would be configured to
HDLC mode to handle the D channel; another IMP SCC would be used to rate adapt the
Example: B1 supports 2 bits; B2 supports 3 bits
SIMASK = $26C0; SIMODE = $01B2
L1RXD
D
A
B1
B2
D
M
L1SY1
L1CLK
L1TXD
B1
D
A
B2
D
M
SMC2
SMC1
SCC1–SCC3
L1TXD
L1RXD
THREE-STATE
DON'T CARE
B1
B1
D
A
B2
D
A
B2
B2
B2
D
M
D
M
2
2
1
SCC2
SCC3
SMC2
SCC1
SCC1
SCC3
SMC1
(CLOCK NOT TO SCALE)
(L1RQ and L1GR not shown)
6
1
2
2
1
1
1
1