Datasheet

122
AT89C5132
4173C–USB–07/04
Configuration The SPI configuration is made through SPCON.
Master Configuration The SPI operates in master mode when the MSTR bit in SPCON is set.
Slave Configuration The SPI operates in slave mode when the MSTR bit in SPCON is cleared and data has
been loaded in SPDAT.
Data Exchange There are two possible Policies to exchange data in master and slave modes:
• polling
• interrupts
Master Mode with Polling
Policy
Figure 100 shows the initialization phase and the transfer phase flows using the polling
policy. Using this flow prevents any overrun error occurrence.
• The bit rate is selected according to Table 97.
• The transfer format depends on the slave peripheral.
•SS
may be deasserted between transfers depending also on the slave peripheral.
• SPIF flag is cleared when reading SPDAT (SPSTA has been read before by the
“end of transfer” check).
This policy provides the fastest effective transmission and is well adapted when commu-
nicating at high speed with other Microcontrollers. However, the procedure may then be
interrupted at any time by higher priority tasks.
Figure 100. Master SPI Polling Policy Flows
SPI Initialization
Polling Policy
Disable Interrupt
SPIE = 0
SPI Transfer
Polling Policy
End Of Transfer?
SPIF = 1?
Select Master Mode
MSTR = 1
Select Bit Rate
program SPR2:0
Select Format
program CPOL & CPHA
Enable SPI
SPEN = 1
Select Slave
Pn.x = L
Start Transfer
Write Data in SPDAT
Last Transfer?
Get Data Received
Read SPDAT
Deselect Slave
Pn.x = H