
DS31256 256-Channel, High-Throughput HDLC Controller
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Register Name:
RHPL
Register Description:
Receive HDLC Maximum Packet Length
Register Address:
0410h
Bit #
7
6
5
4
3
2
1
0
Name
RHPL7
RHPL6
RHPL5
RHPL4
RHPL3
RHPL2
RHPL1
RHPL0
Default
0
Bit #
15
14
13
12
11
10
9
8
Name
RHPL15
RHPL14
RHPL13
RHPL12
RHPL11
RHPL10
RHPL9
RHPL8
Default
0
Note: Bits that are underlined are read-only; all other bits are read-write. This is a globe control; only one per device, not one for each
individual HDLC channel.
Bits 0 to 15/Receive HDLC Packet Length (RHPL0 to RHPL15). If the receive length-detection enable bit is
set to 1, the HDLC engine checks the number of received octets in a packet to see if they exceed the count in this
register. If the length is exceeded, the packet is aborted and the remainder is discarded. The definition of “octet
length” is everything between the opening and closing flags, which includes the address field, control field,
information field, and FCS.
Register Name:
THCDIS
Register Description:
Transmit HDLC Channel Definition Indirect Select
Register Address:
0480h
Bit #
7
6
5
4
3
2
1
0
Name
HCID7
HCID6
HCID5
HCID4
HCID3
HCID2
HCID1
HCID0
Default
0
Bit #
15
14
13
12
11
10
9
8
Name
IAB
IARW
n/a
Default
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 7/HDLC Channel ID (HCID0 to HCID7)
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 14/Indirect Access Read/Write (IARW). When the host wishes to read data from the internal transmit HDLC
definition RAM, this bit should be written to 1 by the host. This causes the device to begin obtaining the data from
the channel location indicated by the HCID bits. During the read access, the IAB bit is set to 1. Once the data is
ready to be read from the THCD register, the IAB bit is set to 0. When the host wishes to write data to the internal
transmit HDLC definition RAM, this bit should be written to 0 by the host. This causes the device to take the data
that is currently present in the THCD register and write it to the channel location indicated by the HCID bits.
When the device completes the write, the IAB is set to 0.
Bit 15/Indirect Access Busy (IAB). When an indirect read or write access is in progress, this read-only bit is set
to 1. During a read operation, this bit is set to 1 until the data is ready to be read. It is set to 0 when the data is
ready to be read. During a write operation, this bit is set to 1 while the write is taking place. It is set to 0 once the
write operation is complete.