TL16PIR552 Datasheet, PDF (42/52 Pages) Texas Instruments – DUAL UART WITH DUAL IrDA AND 1284 PARALLEL PORT

TL16PIR552
DUAL UART WITH DUAL IrDA AND
1284 PARALLEL PORT
SLLS222A – DECEMBER 1995 – REVISED AUGUST 1996
PRINCIPLES OF OPERATION
Table 14. Mode Summary
MODE
000
001
010
011
100
110
111
DESCRIPTION
Centronics (default) mode, forward direction only
Bidirectional Centronics mode
Parallel port data FIFO mode
ECP Parallel port mode
EPP mode
Test mode
Configuration mode
mode switching
Mode switching is only allowed into and out of the modes 000 and 001. All 1284 negotiation takes place in these
two modes. Setting the mode to 011 (ECP Parallel Port mode) causes the hardware to initiate data transfer.
Switching out of modes 011 and 010 in the middle of a transfer or when data remains in the FIFO causes the
transfer to be aborted and the data to be lost.
data compression
The TL16PIR552 supports run length encoded (RLE) decompression in hardware and can transfer compressed
data to a peripheral. Run length encoded (RLE) compression in hardware is not supported. To transfer
compressed data in ECP mode, the compression count is written to the ECPAFIFO and a data byte is written
to the ECPDFIFO.
Compression is accomplished by counting identical bytes and transmitting an RLE byte that indicates how many
times the next byte is to be repeated. Decompression simply intercepts the RLE byte and repeats the following
byte the specified number of times. When a run-length count is received from a peripheral, the subsequent data
byte is replicated that specified number of times. A run-length count of zero specifies that only one byte of data
is represented by the next data byte. A run-length count of 127 indicates that the next byte should be expanded
to 128 bytes. To prevent data expansion, however, run-length counts of zero should be avoided.
The RLE command byte is loaded to the FIFO. Then the logic offloads this command to the decompression
counter to generate the correct number of decompressed data available. The logic asserts PDRQ only when
there are data bytes in the FIFO. Although the command byte is loaded to the FIFO, the PDRQ is not asserted.
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