FDC37M607 datasheet(100/182 Pages) SMSC

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100

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.

An interrupt is generated when:

1. For DMA transfers: When serviceIntr is “0”,

dmaEn is “1” and the DMA TC is received.

2. For Programmed I/O:

When serviceIntr is “0”, dmaEn is “0”,

direction

“0”

and

there

are

writeIntrThreshold or more free bytes in

the

FIFO.

Also,

interrupt

generated when serviceIntr is cleared

“0”

whenever

there

are

writeIntrThreshold or more free bytes in

the FIFO.

b.(1) When serviceIntr is “0”, dmaEn is “0”,

direction

“1”

and

there

are

readIntrThreshold or more bytes in the

FIFO.

Also, an interrupt is generated

when

serviceIntr

cleared

whenever there are readIntrThreshold

or more bytes in the FIFO.

3. When

nErrIntrEn

“0”

and

nFault

transitions

from

high

low

when

nErrIntrEn is set from “1” to “0” and nFault is

asserted.

4. When ackIntEn is “1” and the nAck signal

transitions from a low to a high.

FIFO Operation

The

FIFO

threshold

set

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

Programmed 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.

high value of threshold (i.e. 12) is used with a

"sluggish" system by affording a long latency

period after a service request, but results in

more frequent service requests.

DMA TRANSFERS

DMA transfers are always to or from the

ecpDFifo, tFifo or CFifo.

DMA utilizes the

standard PC DMA services. To use the DMA

transfers, the host first sets up the direction and

state as in the programmed I/O case. Then it

programs the DMA controller in the host with the

desired count and memory address. Lastly it

sets dmaEn to 1 and serviceIntr to 0. The ECP

requests DMA transfers from the host by

activating the PDRQ pin. The DMA will empty

or fill the FIFO using the appropriate direction

and mode. When the terminal count in the DMA

controller is reached, an interrupt is generated

and serviceIntr is asserted, disabling DMA. In

order to prevent possible blocking of refresh

requests dReq shall not be asserted for more

than 32 DMA cycles in a row.

The FIFO is

enabled directly by asserting nPDACK and

addresses

need

not

valid.

PINTR

generated when a TC is received. PDRQ must

FDC37M607 Datasheet(PDF) 100 Page - SMSC Corporation

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