DS31256 datasheet(80/183 Pages) MAXIM

80 / 183 page

DS31256 256-Channel, High-Throughput HDLC Controller

80 of 183

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 write data to the internal transmit starting

block pointer RAM, this bit should be written to 1 by the host. This causes the device to take the data that is in the

TFSBP register and write it to the channel location indicated by the HCID bits. When the device has completed the

write, the IAB is set to 0.

Note: The TFSBP register is write-only memory. Once this register has been written to and the operation has

started, the DS31256 internal state machine changes the value in this memory.

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 has completed.

TFSBP

Transmit FIFO Starting Block Pointer

0984h

Bit #

Name

TSBP7

TSBP6

TSBP5

TSBP4

TSBP3

TSBP2

TSBP1

TSBP0

Default

Bit #

Name

n/a

TSBP9

TSBP8

Default

Note: Bits that are underlined are read-only; all other bits are read-write.

Bits 0 to 9/Starting Block Pointer (TSBP0 to TSBP9). These bits determine which of the 1024 blocks within the

transmit FIFO the host wants the device to configure as the starting block for a particular HDLC channel. Any of

the blocks within a chain of blocks for an HDLC channel can be configured as the starting block. When these bits

are read, they report the current block pointer being used to read data from the transmit FIFO by the HDLC Layer

2 engines.

0000000000 (000h) = use block 0 as the starting block

0111111111 (1FFh) = use block 511 as the starting block

1111111111 (3FFh) = use block 1023 as the starting block

TFBPIS

Transmit FIFO Block Pointer Indirect Select

0990h

Bit #

Name

BLKID7

BLKID6

BLKID5

BLKID4

BLKID3

BLKID2

BLKID1

BLKID0

Default

Bit #

Name

IAB

IARW

n/a

BLKID9

BLKID8

Default

Note: Bits that are underlined are read-only; all other bits are read-write.

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