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ST72321AR6 Datasheet

  • ST72321AR6

  • 8-BIT MCU WITH NESTED INTERRUPTS, FLASH,10-BIT ADC, FIVE TIM...

  • STMicroelectronics   STMicroelectronics

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ST72321
SERIAL PERIPHERAL INTERFACE
(Cont鈥檇)
10.5.5 Error Flags
10.5.5.1 Master Mode Fault (MODF)
Master mode fault occurs when the master device
has its SS pin pulled low.
When a Master mode fault occurs:
鈥?The MODF bit is set and an SPI interrupt re-
quest is generated if the SPIE bit is set.
鈥?The SPE bit is reset. This blocks all output
from the device and disables the SPI periph-
eral.
鈥?The MSTR bit is reset, thus forcing the device
into slave mode.
Clearing the MODF bit is done through a software
sequence:
1. A read access to the SPICSR register while the
MODF bit is set.
2. A write to the SPICR register.
Notes:
To avoid any conflicts in an application
with multiple slaves, the SS pin must be pulled
high during the MODF bit clearing sequence. The
SPE and MSTR bits may be restored to their orig-
inal state during or after this clearing sequence.
Hardware does not allow the user to set the SPE
and MSTR bits while the MODF bit is set except in
the MODF bit clearing sequence.
10.5.5.2 Overrun Condition (OVR)
An overrun condition occurs, when the master de-
vice has sent a data byte and the slave device has
not cleared the SPIF bit issued from the previously
transmitted byte.
When an Overrun occurs:
鈥?The OVR bit is set and an interrupt request is
generated if the SPIE bit is set.
In this case, the receiver buffer contains the byte
sent after the SPIF bit was last cleared. A read to
the SPIDR register returns this byte. All other
bytes are lost.
The OVR bit is cleared by reading the SPICSR
register.
10.5.5.3 Write Collision Error (WCOL)
A write collision occurs when the software tries to
write to the SPIDR register while a data transfer is
taking place with an external device. When this
happens, the transfer continues uninterrupted;
and the software write will be unsuccessful.
Write collisions can occur both in master and slave
mode. See also
Section 10.5.3.2 Slave Select
Management.
Note:
a "read collision" will never occur since the
received data byte is placed in a buffer in which
access is always synchronous with the MCU oper-
ation.
The WCOL bit in the SPICSR register is set if a
write collision occurs.
No SPI interrupt is generated when the WCOL bit
is set (the WCOL bit is a status flag only).
Clearing the WCOL bit is done through a software
sequence (see
Figure 58).
Figure 58. Clearing the WCOL bit (Write Collision Flag) Software Sequence
Clearing sequence after SPIF = 1 (end of a data byte transfer)
1st Step
Read SPICSR
RESULT
2nd Step
Read SPIDR
SPIF =0
WCOL=0
Clearing sequence before SPIF = 1 (during a data byte transfer)
1st Step
2nd Step
Read SPICSR
RESULT
Read SPIDR
WCOL=0
Note:
Writing to the SPIDR regis-
ter instead of reading it does not
reset the WCOL bit
93/185

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