selected as source, the null device is always ready and sends the data (2 bytes) of the
initialized CRC value MSB first.
Channel Priority
The Data Flow Controller bandwidth is shared between Channel 0 and Channel 1. In
case both channels are ready to transfer data, bus bandwidth is shared on a byte by
byte basis.
In order to allocate maximum bandwidth to a specified channel, priority can be assigned
to channel 0 or to channel 1 by setting the DFPRIO1:0 bits in DFCON according to
Table 93.
DFPRIO1:0 can be modified at any time while transfer is on-going or not.
Table 93. Channel Priority Assignment
DFPRIO1
DFPRIO0 Assignment Description
0
0
1
1
0
1
0
1
No priority assigned: channel 0 & channel 1 have same priority.
Priority assigned to channel 0.
Priority assigned to channel 1.
Reserved, do not set both bits.
Data Flow Status
Data Flow Abort
An on-going data flow transfer is reported to user using the bits DFBSY0 and DFBSY1
in DFCSTA. These bits are set as soon as the DFD has been fully written to the corre-
sponding channel and cleared at the end of transfer or abort.
Source peripheral and destination peripheral status is dynamically reported by SRDY0,
DRDY0, SRDY1, DRDY1 ready flags in DFCSTA.
The DFC allows asynchronous abort of any on-going flow. Abort is controlled by the
DFABT0, DFABT1, the Channel Data Flow Abort control bits in DFCCON and DFABTM
the Data Flow Abort Mode control bit in DFCON.
Setting DFABT0 or DFABT1 while a flow transfer is on-going triggers on the correspond-
ing channel an immediate or delayed abort depending on the DFABTM value. DFABTM
cleared triggers an immediate abort where data flow transfer is stopped at the end of the
on-going byte transfer while DFABTM set triggers a delayed abort where data flow
transfer is stopped at the end of the on-going data packet transfer. Above abort modes
set the End of Flow interrupt flag of the corresponding channel.
Setting DFABT0 or DFABT1 while a DFD is under writing will reset the DFD content of
the corresponding channel. Such abort does not set the End of Flow interrupt flag of the
corresponding channel.
Abort Status
In case a data flow transfer is aborted, the remaining number of data packets to be
transmitted can be retrieved by reading two bytes with MSB first from the data flow
descriptor register DFD0 (channel 0) or to DFD1 (channel 1). This feature is of interest
in case of logical data flow management over a physical channel.
Note:
In case of immediate abort, returned value is not significant since part of the DP is
already transmitted.
80
AT85C51SND3Bx
7632A–MP3–03/06
ATMEL [ ATMEL ]
