DS31256 256-Channel, High-Throughput HDLC Controller
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Bit 15/Receive DS0 Channel Enable (RCHEN). This bit must be set for each active DS0 channel in a
channelized application. In a channelized application, although a DS0 channel is deactivated, the channel can still
be set up to route data to the V.54 detector and/or the BERT block. In addition, although a DS0 channel is active,
the loopback function (CLLB = 1) overrides this activation and routes transmit data back to the HDLC controller
instead of the data coming in through the RD pin. In an unchannelized mode (RUEN = 1), only the RCHEN bit in
R[n]CFG0 needs to be configured.
0 = deactivated DS0 channel
1 = active DS0 channel
Register Name:
T[n]CFG[j], where n = 0 to 15 for each port and j = 0 to 127 for each DS0
Register Description:
Transmit Layer 1 Configuration Register
Register Address:
Indirect Access through CP[n]RD
Bit #
7
6
5
4
3
2
1
0
Name
TCH#(8): Transmit HDLC Channel Number
Default
Bit #
15
14
13
12
11
10
9
8
Name
TCHEN
TBERT
n/a
CNLB
n/a
TFAO
T56
Default
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 7/Transmit Channel Number (TCH#). The CPU loads the number of the HDLC channels associated
with this particular DS0 channel. If the port is running in an unchannelized mode (TUEN = 1), the HDLC channel
number only needs to be loaded into T[n]CFG0. If the fast (52Mbps) HDLC engine is enabled on port 0, HDLC
channel 1 is assigned to it and, likewise, HDLC channel 2 is assigned to the fast HDLC engine on port 2, if it is
enabled. Therefore, these HDLC channel numbers should not be used if the fast HDLC engines are enabled.
00000000 (00h) = HDLC channel number 1 (also used for the fast HDLC engine on port 0)
00000001 (01h) = HDLC channel number 2 (also used for the fast HDLC engine on port 1)
00000010 (02h) = HDLC channel number 3 (also used for the fast HDLC engine on port 2)
00000011 (03h) = HDLC channel number 4
11111111 (FFh) = HDLC channel number 256
Bit 8/Transmit 56kbps (T56). If the port is running a channelized application, this bit determines whether or not
the LSB of each DS0 should be processed. If this bit is set, the LSB of each DS0 channel is not routed from the
HDLC controller (or the BERT, if it has been enabled through the RBERT bit), and the LSB bit position is forced
to 1.
0 = 64kbps (use all 8 bits in the DS0)
1 = 56kbps (use only the first 7 bits transmitted in the DS0; force the LSB to 1)
Bit 9/Transmit Force All Ones (TFAO). If this bit is set, then eight 1s are placed into the DS0 channel for
transmission instead of the data that is being sourced from the HDLC controller. If this bit is cleared, the data from
the HDLC controller is transmitted. This bit is useful in instances when CLLB is being activated to keep the
looped back data from being sent out onto the network. This bit overrides TCHEN.
0 = transmit data from the HDLC controller
1 = force transmit data to all 1s
Bit 11/Channelized Network Loopback Enable (CNLB). Enabling this loopback forces the receive data to
replace the transmit data. This bit must be set for each and every DS0 channel that is to be looped back. This bit
overrides TBERT, TFAO, and TCHEN.
0 = loopback disabled
1 = loopback enabled