at7601fg AME, Inc., at7601fg Datasheet - Page 21

• Manufacturer Part Number: at7601fg
• Description: Printer Port Controller
• Manufacturer: AME, Inc.

Rev. B.02
AT7601F
5-3-2.7 Interrupts
5-3-2.8 FIFO Operation
Servicelntr = 1 Disables the DMA and all of the service interrupts.
An interrupt is generated when:
1. For DMA transfers: When Servicelntr is 0, DMAEn is 1and the DMA TC is received.
4. When AckIntEn is 1 and the ACK# signal transitions from a low to a high.
The interrupts are enabled by Servicelntr in the ECR register.
Servicelntr = 0 Enables the selected interrupt condition. If the interrupting condition is valid, then the
interrupt is generated immediately when this bit is changed from a 1 to a 0. This can occur during
Programmed I/O if the number of bytes removed or added from/to the FIFO does not cross the threshold.
The interrupt generated is ISA friendly in that it must pulse the interrupt line low, allowing for interrupt
sharing. After a brief pulse low following the interrupt event, the interrupt line is tri-stated so that
other interrupts may assert.
2. For Programmed I/O:
3. When ErrIntrEn# is 0 and Fault# transitions from high to low or when ErrIntrEn# is set from 1 to 0 and
The FIFO threshold is set in the chip configuration registers. All data transfers to or from the parallel port
can proceed in DMA or Programmed I/O (non-DMA) mode as indicated by the selected mode. The FIFO
is used by selecting the Parallel Port FIFO mode or ECP Parallel Port Mode. (FIFO test mode will be
addressed separately.) After a reset, the FIFO is disabled. Each data byte is transferred by a Pro-
grammed I/O cycle or PDRQ depending on the selection of DMA or Programmed I/O mode.
The following paragraphs detail the operation of the FIFO flow control. In these descriptions, <threshold>
ranges from 1 to 16. The parameter FIFOTHR, which the user programs, is one less and ranges from 0 to
15.
A low threshold value (i.e.2) results in longer periods of time between service requests, but requires faster
servicing of the request for both read and write cases. The host must be very responsive to the service
request. This is the desired case for use with a "fast" system.
A high value of threshold (i.e.2) is used with a "sluggish" system by affording a ling latency period after a
service request, but results in more frequent service requests.
AME, Inc.
a. When Servicelntr is 0, DMAEn is 0, direction is 0 and there are writeIntrThreshold or more free
b. When Servicelntr is 0, DMAEn is 0, direction is 1 and there are readlntrThreshold or more bytes
ErrIntrEn# is set from 1 to 0 and Fault# is asserted.
bytes in the FIFO. Also, an interrupt is generated when Servicelntr is cleared to 0 whenever there
in the FIFO. Also, an interrupt is generated when Servicelntr is cleared to 0 whenever
are writeIntrThreshold or more free bytes in the FIFO.
there are readlntrThreshold or more bytes in the FIFO
Printer Port Controller
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