BITS 6 and 7 during a read are a low level, and cannot be written.
CFIFO (Parallel Port Data FIFO)
ADDRESS OFFSET = 400h
Mode = 010
Bytes written or DMAed from the system to this FIFO are transmitted by a hardware handshake to the peripheral using
the standard parallel port protocol. Transfers to the FIFO are byte aligned. This mode is only defined for the forward
direction.
ECPDFIFO (ECP Data FIFO)
ADDRESS OFFSET = 400H
Mode = 011
Bytes written or DMAed from the system to this FIFO, when the direction bit is 0, are transmitted by a hardware
handshake to the peripheral using the ECP parallel port protocol. Transfers to the FIFO are byte aligned.
Data bytes from the peripheral are read under automatic hardware handshake from ECP into this FIFO when the
direction bit is 1. Reads or DMAs from the FIFO will return bytes of ECP data to the system.
TFIFO (Test FIFO Mode)
ADDRESS OFFSET = 400H
Mode = 110
Data bytes may be read, written or DMAed to or from the system to this FIFO in any direction. Data in the tFIFO will not
be transmitted to the to the parallel port lines using a hardware protocol handshake. However, data in the tFIFO may be
displayed on the parallel port data lines.
The tFIFO will not stall when overwritten or underrun. If an attempt is made to write data to a full tFIFO, the new data is
not accepted into the tFIFO. If an attempt is made to read data from an empty tFIFO, the last data byte is re-read again.
The full and empty bits must always keep track of the correct FIFO state. The tFIFO will transfer data at the maximum
ISA rate so that software may generate performance metrics.
The FIFO size and interrupt threshold can be determined by writing bytes to the FIFO and checking the full and
serviceIntr bits.
The writeIntrThreshold can be determined by starting with a full tFIFO, setting the direction bit to 0 and emptying it a byte
at a time until serviceIntr is set. This may generate a spurious interrupt, but will indicate that the threshold has been
reached.
The readIntrThreshold can be determined by setting the direction bit to 1 and filling the empty tFIFO a byte at a time until
serviceIntr is set. This may generate a spurious interrupt, but will indicate that the threshold has been reached.
Data bytes are always read from the head of tFIFO regardless of the value of the direction bit. For example if 44h, 33h,
22h is written to the FIFO, then reading the tFIFO will return 44h, 33h, 22h in the same order as was written.
CNFGA (Configuration Register A)
ADDRESS OFFSET = 400H
Mode = 111
This register is a read only register. When read, 10H is returned. This indicates to the system that this is an 8-bit
implementation. (PWord = 1 byte)
CNFGB (Configuration Register B)
ADDRESS OFFSET = 401H
Mode = 111
BIT 7 Compress
This bit is read only. During a read it is a low level. This means that this chip does not support hardware RLE
compression. It does support hardware de-compression.
SMSC DS – LPC47M14X
Page 88
Rev. 03/19/2001
SMSC [ SMSC CORPORATION ]
