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Parallel Port Interface
9-14
MC68322 USER’S MANUAL
MOTOROLA
9.7 PPI ON RESET
The assertion of RESET causes all PPI registers and register fields to be cleared to zero
(with one exception). The BSY2 bit in the PPIR is set and remains that way until the software
explicitly clears it. This is intended to delay the host long enough for the software to initialize
the PPI.
The RST bit in the PPCR resets the PPI state machine, which includes the hardware
handshake controller and run-length decompression logic. Normally, when RST is set,
MODE is set to 002 to prevent the state machine from starting again. RST immediately
causes the handshake controller and the run-length decompression logic to return to idle.
The handshake controller immediately discontinues handshaking with the host, terminates
decompression, and any pending DMA request is removed. When the PPI state machine is
in the idle state, BUSY and ACK are negated. If BSY2 and ACK2 are clear, then BSY1 will
be cleared and ACK1 will be set. RST also clears RLD and FLL bits in the PPCR. The
software should issue RST under error conditions, such as when an invalid transition
interrupt occurs or when the software detects a time-out error.
9.8 PPI DATA TRANSFER RATE
The expected data transfer rate in a system depends on several factors—capability of the
host computer, memory speed, and bandwidth used. The block size of the data transfer
affects the data rate because of the overhead involved. Forward data transfers are DMA
based and reverse data transfers are interrupt based. Overhead cycles such as the
negotiation phases are also interrupt based. The following are expected data transfer rates.
Compatibility mode (forward) data rate = 400K/sec. Actually, the PPI is capable of a
compatibility mode forward data rate of 2M/sec. The 400K/sec is determined by the
IEEE 1284 specification.
ECP mode (forward) data rate = 2M/sec.
ECP decompression (forward) data rate = 4M/sec.
Nibble mode (reverse) data rate = 5K/sec.
Byte mode (reverse) data rate = 10K/sec.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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