
DS3134
91 of 203
Register Description: Receive FIFO High Water Mark Indirect Select
Register Address:
0920h
76
5432
10
HCID7
HCID6
HCID5
HCID4
HCID3
HCID2
HCID1
HCID0
15
14
13
12
11
10
9
8
IAB
IARW
n/a
Note: Bits that are underlined are read only, all other bits are read-write; default value for all bits is 0.
Bits 0 to 7 / HDLC Channel ID (HCID0 to HCID7).
00000000 (00h) = HDLC Channel Number 1
11111111 (FFh) = HDLC Channel Number 256
Bit 14 / Indirect Access Read/Write (IARW). When the host wishes to read data from the internal
Receive High Water Mark RAM, this bit should be written to a one 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 will be set to one. Once the data is ready to be read from the RFHWM register, the IAB bit
will be set to zero. When the host wishes to write data to the internal Receive High Water Mark RAM,
this bit should be written to a zero by the host. This causes the device to take the data that is currently
present in the RFHWM register and write it to the channel location indicated by the HCID bits. When the
device has completed the write, the IAB will be set to zero.
Bit 15 / Indirect Access Busy (IAB). When an indirect read or write access is in progress, this read only
bit will be set to a one. During a read operation, this bit will be set to a one until the data is ready to be
read. It will be set to zero when the data is ready to be read. During a write operation, this bit will be set
to a one while the write is taking place. It will be set to zero once the write operation has completed.
Register Name:
RFHWM
Register Description: Receive FIFO High Water Mark
Register Address:
0924h
7
6
54
32
10
RHWM7
RHWM6
RHWM5
RHWM4
RHWM3
RHWM2
RHWM1
RHWM0
15
14
13
12
11
10
9
8
n/a
RHWM9
RHWM8
Note: Bits that are underlined are read only, all other bits are read-write.
Bits 0 to 9 / High Water Mark (RHWM0 to RHWM9). These 10 bits indicate the setting of the
Receive High Water Mark. The High Water Mark setting is the number of successive blocks that the
HDLC engine will write to the FIFO before the DMA will send the data to the PCI Bus. The High Water
Mark setting must be between (inclusive) one block and one less than the number of blocks in the link-list
chain for the particular channel involved. For example, if four blocks are linked together, then the High
Water Mark can be set to 1, 2 or 3. In another words the High Water Mark can be set to a value of 1 to N
– 1, where N = number of blocks are linked together. Any other numbers are illegal.
0000000000 (000h) = invalid setting
0000000001 (001h) = High Water Mark is 1 Block