Datasheet

88
AT89C51AC3
4383D–8051–02/08
When a transmission is in progress a new data can be queued and sent as soon as
transmission has been completed. So it is possible to transmit bytes without latency,
useful in some applications.
The SPTE bit in SPSCR is set as long as the transmission buffer is free. It means that
the user application can write SPDAT with the data to be transmitted until the SPTE
becomes cleared.
Figure 49 shows a queuing transmission in master mode. Once the Byte 1 is ready, it is
immediately sent on the bus. Meanwhile an other byte is prepared (and the SPTE is
cleared), it will be sent at the end of the current transmission. The next data must be
ready before the end of the current transmission.
Figure 49. Queuing Transmission In Master Mode
In slave mode it is almost the same except it is the external master that start the
transmission.
Also, in slave mode, if no new data is ready, the last value received will be the next data
byte transmitted.
MSB
B6 B5 B4 B3 B2
B1
LSB
MOSI
SCK
MSB
B6 B5 B4 B3 B2
B1
LSB
BYTE 1 under transmission
MSB
B6 B5 B4 B3 B2
B1
LSB
MSB
B6 B5 B4 B3 B2
B1
LSB
MISO
Data
Byte 1 Byte 2
Byte 3
SPTE
BYTE 2 under transmission