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DS3134
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Bit 0 / Receive DMA Enable (RDE). This bit is used to enable the receive DMA. When it is set to zero,
the receive DMA will not pass any data from the receive FIFO to the PCI Bus even if there is one or more
HDLC channels enabled.
On device initialization, the Host should fully configure the receive DMA
before enabling it via this bit.
0 = receive DMA is disabled
1 = receive DMA is enabled
Bit 1 / Receive DMA Throttle Select Bit 0 (RDT0).
Bit 2 / Receive DMA Throttle Select Bit 1 (RDT1).
These two bits select the maximum burst length that the receive DMA is allowed on the PCI Bus. The
DMA can be restricted to a maximum burst length of just 32 dwords (128 bytes) or it can be
incrementally adjusted up to 256 dwords (1024 bytes). The Host will select the optimal length based on a
number of factors including the system environment for the PCI Bus, the number of HDLC channels
being used, and the trade off between channel latency and bus efficiency.
00 = burst length maximum is 32 dwords
01 = burst length maximum is 64 dwords
10 = burst length maximum is 128 dwords
11 = burst length maximum is 256 dwords
Bit 3 / Transmit DMA Enable (TDE). This bit is used to enable the transmit DMA. When it is set to
zero, the transmit DMA will not pass any data from the PCI Bus to the transmit FIFO even if there is one
or more HDLC channels enabled.
On device initialization, the Host should fully configure the transmit
DMA before enabling it via this bit.
0 = transmit DMA is disabled
1 = transmit DMA is enabled
Bit 4 / Transmit DMA Throttle Select Bit 0 (TDT0).
Bit 5 / Transmit DMA Throttle Select Bit 1 (TDT1).
These two bits select the maximum burst length that the transmit DMA is allowed on the PCI Bus. The
DMA can be restricted to a maximum burst length of just 32 dwords (128 bytes) or it can be
incrementally adjusted up to 256 dwords (1024 bytes). The Host will select the optimal length based on a
number of factors including the system environment for the PCI Bus, the number of HDLC channels
being used, and the trade off between channel latency and bus efficiency.
00 = burst length maximum is 32 dwords
01 = burst length maximum is 64 dwords
10 = burst length maximum is 128 dwords
11 = burst length maximum is 256 dwords
Bit 6 / PCI Bus Orientation (PBO).
This bit selects whether HDLC packet data on the PCI Bus will operate in either Little Endian format or
Big Endian format. Little Endian byte ordering places the least significant byte at the lowest address
while Big Endian places the least significant byte at the highest address. This bit setting only affects
HDLC data on the PCI Bus. All other PCI Bus transactions to the internal device configuration registers,
PCI configuration registers, and Local Bus, are always in Little Endian format.
0 = HDLC Packet Data on the PCI Bus is in Little Endian format
1 = HDLC Packet Data on the PCI Bus is in Big Endian format