am79c30a Advanced Micro Devices, am79c30a Datasheet - Page 20

• Manufacturer Part Number: am79c30a
• Description: Digital Subscriber Controller ?dsc ?circuit
• Manufacturer: Advanced Micro Devices

The three D-channel loopback controls defined in
LMR2 bits 0, 1, and 2 are explained below:
Bit 0, D-channel loopback at Am79C30A/32A enable:
This remote loopback is provided for maintenance pur-
poses from the NT’s perspective. The NT transmits
D-channel bits to the Am79C30A/32A where they are
internally looped (with the Data Link Controller) and
transmitted back to the NT. The incoming D-channel
data can be accessed by the microprocessor; however,
the microprocessor cannot send data on the outgoing
D channel.
Any difference between the transmitted D-channel bits
a n d t h e r e c e i ve d E - c h a n n e l b i t s t o / f r o m t h e
Am79C30A/32A (normally detected as an error which
halts the transmission) is ignored, thereby allowing the
transmission to continue.
Multiframe Register (MF), Read/Write
Address = Indirect A6H
20
5, 6
Am79C30A
Bit
0
1
2
3
4
7
Logical 1
Enable Multiframe sync
Enable S-data available interrupt
Enable Q-bit buffer empty interrupt
Enable Multiframe change of state interrupt
First subframe
Not used, reads logical 0
Multiframe synchronized (read only)
D
D
S
E
D
D
NT/PABX
Table 14. Multiframe Register
Am79C30A/32A Data Sheet
Bit 1, D-channel loopback at LIU enable:
This local loopback is provided for local testing. Data on
the incoming D channel is ignored. The data from the
microprocessor is processed by the DLC and then
looped back to the microprocessor.
Bit 2, D-channel back-off disable:
This loopback is provided for maintenance purposes
from the TE’s perspective. The Am79C30A/32A trans-
mits D-channel bits to the NT where they are looped
and transmitted back to the Am79C30A/32A in the E
channel. The operation is normal except differences
between the D and E channels do not halt the trans-
mission.
Disable interrupt
Not used, reads logical 0
Multiframe not synchronized (read only)
Logical 0 (Default Value)
Disable Multiframe sync
Disable interrupt
Disable interrupt
Not first subframe
Am79C30A
Am79C30A
MPI
D
E
D
S
S
D
NT/PABX
D
E
NT/PABX