CD1284 Datasheet, PDF (139/176 Pages) Intel Corporation – IEEE 1284-Compatible Parallel Interface Controller with Two High-Speed Asynchronous Serial Ports

IEEE 1284-Compatible Parallel Interface Controller — CD1284
Bits
7:3
2:0
7.7.6
Description
User-defined Interrupt Vector: Host software can use these five bits for any purpose appropriate to the
application. In some cases, these bits might define the rest of a complete interrupt response vector (Motorola-
type systems). In the case of daisy-chain systems made up of multiple CD1284s, these bits define the device
number in the chain.
Interrupt Vector Type Code: These bits are read/writable in the normal context. These bits are ‘don’t cares’.
Parallel Auxiliary Control Register
Register Name: PACR
Register Description: Parallel Auxiliary Control
Access: Read/Write
Bit 7
Bit 6
Bit 5
ShrtTen
ShrtStal
StaleOff
Bit 4
FIFOlock
Bit 3
ClearTO
Bit 2
0
8-Bit Hex Address: 3F
Default Value: 00
Bit 1
AsyncDMA
Bit 0
Unfair
This register provides some special functions for the parallel data path and interrupt generation
circuitry. The upper two bits change the basic timing of the timers associated with the data pipeline.
Bit 5 can disable the stale data timer. Bit 0 overrides the Fair Share functions of the device (serial
and parallel channels).
Bit
Description
ShrtTen: This function shortens the Prescaler count cycle that generates the internal 10-µs (based on a 25-
7
MHz system clock) clock for the stale data counter. This bit is cleared by RESET*. If set, the 10-µs ‘ticks’ of
the counter are generated every two CLKs; the normal period is one ‘tick’ every 250 CLKs.
ShrtStal: This function shortens the period of the stale data timer. The stale data timer includes a divide-by-
10 prescaler; setting this bit bypasses the prescaler function thus causing the stale data timer to count on
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each 10-µs clock ‘tick’.
If both ShrtTen and ShrtStal are set, the stale data timer counts on every other CLK.
StaleOff: If set, this bit masks off the Stale Status bit. The inverse of this bit is AND’ed with the stale state
5
condition of the parallel channel to produce the stale status and disables OneChar and Stale as interrupt
sources. StaleOff is provided primarily for test and development purposes if slow movement of data into the
parallel port causes Stale and OneChar to always appear true.
FIFOlock: The FIFOlock bit causes the FIFO to stop accepting data from the parallel channel state machine.
This action makes the FIFO appear full to the parallel port, thus causing it to enter the ‘busy’ state. This
function is primarily intended for use in system testing to cause a timeout on the 1284 bus.
4
Setting this bit in ECP Forward mode may cause a stall condition event 35 because event 36 does not occur
until FIFOlock is cleared. The ECP mode host transfer recovery handshake sequence (from event 35 stall) is
supported and the byte transit discarded as required by the specification. This bit does not provide an
effective means to flow control the host.
Clear Timeout: This bit is a reset bit for the timeout status latch logic. When toggled by software, the timeout
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status in the PFSR is cleared; it may be left set to disable the Timeout status function. Note that if this bit is
left set, the OneChar interrupt condition will never become true because the OneChar interrupt logic uses the
timeout status to determine when the FIFO has become stale.
Datasheet
139