Instruction Manual

66 DS271F5
CS8900A
Crystal LAN™ Ethernet Controller
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ResetRxDMA When set, the RxDMA offset pointer at PacketPage base + 0026h is reset to zero. When the
host sets this bit, the CS8900A does the following:
1.Terminates the current receive DMA activity, if any.
2.Clears all internal receive buffers.
3.Zeroes the RxDMA offset pointer.
DMAextend When set, DMARQx goes inactive on the falling edge of IOR
N
instead of the rising edge of
IOR
N-1
. See Switching Characteristics, DMA Read, t
DMAR5
. Setting this bit also enables single
transfer mode DMA. Normal operation is demand mode DMA in which DMACKx cannot deas-
sert until after DMARQx deasserts, i.e. until a full ethernet frame is transferred. Single transfer
mode allows DMACKx to deassert between each DMA read.
UseSA When set, the MEMCS16
pin goes low whenever the address on SA bus [12..19] match the
CS8900A's assigned Memory base address and the CHIPSEL
pin is low (internal address de-
code).
When clear, MEMCS16
is driven low whenever CHIPSEL goes low. (external address decode).
see Section 4.9 on page 73.
For MEMCS16
pin to be enabled, the CS8900A must be in Memory Mode with the MemoryE
bit (Register 17, BusCTL, Bit A) set.
MemoryE When set, the CS8900A may operate in Memory Mode. When clear, Memory Mode is disabled.
I/O Mode is always enabled.
DMABurst When clear, the CS8900A performs continuous DMA until the receive frame is completely
transferred from the CS8900A to host memory. When set, each DMA access is limited to 28us,
after which time the CS8900A gives up the bus for 1.3us before making a new DMA request.
IOCHRDYE When set, the CS8900A does not use the IOCHRDY output pin, and the pin is always high-im-
pedance. This allows external pull-up to force the output high. When clear, the CS8900A drives
IOCHRDY low to request additional time during I/O Read and Memory Read cycles. IOCHRDY
does not affect I/O Write, Memory Write, nor DMA Read.
RxDMAsize This bit determines the size of the receive DMA buffer (located in host memory). When set, the
DMA buffer size is 64 Kbytes. When clear, it is 16 Kbytes.
EnableRQ When set, the CS8900A will generate an interrupt in response to an interrupt event
(Section 5.1). When cleared, the CS8900A will not generate any interrupts.
After reset, if no EEPROM is found by the CS8900A, then the register has the following initial state. If an EEPROM
is found, then the register's initial value may be set by the EEPROM. See Section 3.3 on page 19.
Reset value is: 0000 0000 0001 0111
4.4.21 Register 18: Bus Status
(BusST, Read-only, Address: PacketPage base + 0138h)
BusST describes the status of the current transmit operation.
011000 These bits provide an internal address used by the CS8900A to identify this as the Bus Status
76543210
TxBidErr 011000
FEDCBA9 8
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