SCD1284 INTEL [Intel Corporation], SCD1284 Datasheet - Page 82

• Manufacturer Part Number: SCD1284
• Description: IEEE 1284-Compatible Parallel Interface Controller with Two High-Speed Asynchronous Serial Ports
• Manufacturer: INTEL [Intel Corporation]

CD1284 — IEEE 1284-Compatible Parallel Interface Controller
5.13
5.13.1
5.13.2
5.13.3
5.13.4
82
1284 Parallel Protocol Support
Compatibility Mode
Compatibility mode provides backward compatibility with Centronics and PC-compatible printer
interfaces. When the host parallel port is in Compatibility mode (with no data transfer in progress),
the host can initiate data transfers in Compatibility mode or initiate negotiations to a new operating
mode.
Only Busy-while-Strobe and Ack-in-Busy timing is supported in Compatibility mode. Busy-after-
Strobe, Ack-after-Busy, and Ack-while-Busy timings are not supported.
Reverse-Nibble and Reverse-Byte Modes
These modes support reverse transfers only, from slave to master. Reverse-Nibble mode is enabled
with NER[0]; Reverse-Byte mode is enabled with NER[1]. Reverse-Nibble mode sends 4 bits at a
time over four of the peripheral status lines. With software drivers the advantage of this scheme is
that any unidirectional PC parallel port can be used for bidirectional data transfers. Reverse-Byte
mode requires bidirectional buffers on the PC hardware, but allows substantially faster transfers
because it moves one byte at a time.
There is no mechanism in Compatibility mode for the slave to indicate that data is available for
reverse transfers. The master must poll the slave by negotiating into a reverse mode and examining
the nDatAv signal. During negotiation, RevRq (SCR[0]) instructs the CD1284 to post the
availability of data to the master through the nDatAv signal.
ID Request
An ID request is enabled with a combination of NER[6] and one of four other transfer mode bits.
ID requests can be made in conjunction with ECP, ECP/RLE, Reverse-Byte, and Reverse-Nibble
modes; there is no ID request function defined for EPP mode. The CD1284 can accept an ID
request in any mode where it is enabled to do transfers. IDReq is set when an ID request is received
in any enabled mode.
ECP Mode
ECP mode allows bidirectional transfers and supports the RLE-compression scheme. The ability to
expand RLE data is required of all IEEE-1284, ECP-compliant devices, but the ability to compress
data is optional. The CD1284 handles both expansion and compression in the data path section.
The parallel port simply passes the inverse of the command signal to/from the FIFO on the ninth
tag bit in the FIFO. ECP mode is enabled by NER[2]. RLE mode enabling requires both NER bits
2 and 3.
nStrobe
BUSY
nAck
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