IRCC SMSC Corporation, IRCC Datasheet - Page 66

• Manufacturer Part Number: IRCC
• Description: INFRARED COMMUNICATIONS CONTROLLER
• Manufacturer: SMSC Corporation

with asynchronous Host/ SCE access timing, and
during loopback tests with synchronous SCE-
only access timing
simultaneouly used for transmit and receive.
FIFO controls include, separate read/ write lines,
FIFO Full and FIFO Not Empty flags, Reset,
FIFO Threshold, and Interrupt.
FIFO Threshold
Description
The
programmed
accommodate systems with widely varying I/O
response times. FIFO Threshold values typically
reflect the overall I/O response characteristics of
a system.
used for both I/O read and I/O write cases.
During DMA operatons, the FIFO Threshold is
only used to trigger the SCE transmitter.
The FIFO Threshold value is programmable from
0 to 127. The FIFO Threshold Register, located
in Register Block One, Address Two, contains
the FIFO Threshold value. Low threshold values
result in longer periods of time between service
requests because more of the FIFO is utilized
before the request is issued.
program low threshold values must typically
provide fast response times to these requests;
i.e., high performance systems that move I/O
data quickly.
High threshold values are used in "sluggish"
systems with long service request latencies. Low
performance systems typically take longer to
move I/O data and require more frequent I/O
service.
threshold values, much less of the FIFO is
utilized before service requests are issued.
Receive Threshold
Once the FIFO Interrupt is enabled, Receive
Service
transfers from the FIFO to the host, are
SCE
For systems that program high FIFO
Requests
The same threshold value can be
FIFO
I/O
(RxServReq),
service
Threshold
where the FIFO is
requests
Systems that
i.e.
generates
data
to
66
FIFO Threshold value or more data bytes in the
FIFO, given by:
For example, if the FIFO Threshold value is 12,
RxServReq will be active whenever there 116 to
128 data bytes in the FIFO.
Threshold is 0, RxServReq will be active
whenever the FIFO is full. If the FIFO Threshold
is 127, RxServReq will be active whenever the
FIFO is not empty.
Transmit Threshold
Once the FIFO Interrupt is enabled, Transmit
Service
transfers from the host to the FIFO, are
generated whenever there are FIFO Threshold
value or fewer data bytes in the FIFO, given by:
For example, if the FIFO Threshold value is 12,
TxServReq will be active whenever there are 12
or less data bytes in the FIFO.
Threshold is 0, TxServReq will be active
whenever the FIFO is empty.
Threshold value is 127, TxServReq will be active
whenever the FIFO is not full.
FIFO Interrupt
The FIFO Interrupt becomes active whenever the
FIFO Interrupt Enable is active and either
TxServReq or RxServReq is active. When FIFO
Interrupt Enable becomes inactive, the FIFO
Interrupt goes inactive.
For example, the FIFO Interrupt will become
active during a transmit operation if the FIFO
Threshold is fifty, the FIFO Interrupt Enable is
active, and there are from one to fifty data bytes
in the FIFO (Figure 35).
In Figure 35, notice that five bytes are written to
the FIFO every time a service request is
answered. The third request occurs as soon as
the FIFO Interrupt Enable is activated because
RxServReq ≥ 128 - FIFO Threshold
TxServReq ≤ FIFO Threshold
Requests
(TxServReq),
If the FIFO
If the FIFO
If the FIFO
i.e.
data