参数资料
型号: ST7FLITE19BF0B6
厂商: STMICROELECTRONICS
元件分类: 微控制器/微处理器
英文描述: 8-BIT, FLASH, 8 MHz, MICROCONTROLLER, PDIP20
封装: 0.300 INCH, ROHS COMPLIANT, PLASTIC, DIP-20
文件页数: 150/159页
文件大小: 2855K
代理商: ST7FLITE19BF0B6
ST7LITE1xB
90/159
SERIAL PERIPHERAL INTERFACE (cont’d)
11.4.5 Error Flags
11.4.5.1 Master Mode Fault (MODF)
Master mode fault occurs when the master de-
vice’s SS pin is pulled low.
When a Master mode fault occurs:
– The MODF bit is set and an SPI interrupt re-
quest is generated if the SPIE bit is set.
– The SPE bit is reset. This blocks all output
from the device and disables the SPI periph-
eral.
– 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.
In a slave device, the MODF bit can not be set, but
in a multimaster configuration the device can be in
slave mode with the MODF bit set.
The MODF bit indicates that there might have
been a multimaster conflict and allows software to
handle this using an interrupt routine and either
perform a reset or return to an application default
state.
11.4.5.2 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:
– 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.
11.4.5.3 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 0.1.3.2 Slave Select Man-
agement.
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 CPU 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 6).
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
Read SPIDR
2nd Step
SPIF = 0
WCOL = 0
Clearing sequence before SPIF = 1 (during a data byte transfer)
1st Step
2nd Step
WCOL = 0
Read SPICSR
Read SPIDR
Note: Writing to the SPIDR register in-
stead of reading it does not reset the
WCOL bit.
RESULT
1
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