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SERIAL PERIPHERAL INTERFACE (Cont’d)
14.4.4.4 Write Collision Error
A write collision occurs when the software tries to
write to the DR register while a data transfer is tak-
ing place with an external device. When this hap-
pens, the transfer continues uninterrupted; and
the software write will be unsuccessful.
Write collisions can occur both in master and slave
mode.
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.
In Slave mode
When the CPHA bit is set:
The slave device will receive a clock (SCK) edge
prior to the latch of the first data transfer. This first
clock edge will freeze the data in the slave device
DR register and output the MSBit on to the exter-
nal MISO pin of the slave device.
The SS
pin low state enables the slave device but
the output of the MSBit onto the MISO pin does
not take place until the first data transfer clock
edge.
When the CPHA bit is reset:
Data is latched on the occurrence of the first clock
transition. The slave device does not have any
way of knowing when that transition will occur;
therefore, the slave device collision occurs when
software attempts to write the DR register after its
SS
pin has been pulled low.
For this reason, the SS
pin must be high, between
each data byte transfer, to allow the CPU to write
in the DR register without generating a write colli-
sion.
In Master mode
Collision in the master device is defined as a write
of the DR register while the internal serial clock
(SCK) is in the process of transfer.
The SS
pin signal must be always high on the
master device.
WCOL bit
The WCOL bit in the SR 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 46).
Figure 46. Clearing the WCOL bit (Write Collision Flag) Software Sequence
Clearing sequence after SPIF = 1 (end of a data byte transfer)
1st Step
Read SR
Read DR Write DR
2nd Step
SPIF =0
WCOL=0
SPIF =0
WCOL=0
if no transfer has started
WCOL=1 if a transfer has started
Clearing sequence before SPIF = 1 (during a data byte transfer)
1st Step
2nd Step
WCOL=0
before the 2nd step
Read SR
Read DR
Note: Writing to the DR register
instead of reading in it does not
reset the WCOL bit
Read SR
OR
THEN
THEN
THEN
- ST72334J/N 1
- ST72314J/N, ST72124J 1
- Table of Contents 2
- 2 INTRODUCTION 6
- 3 PIN DESCRIPTION 7
- (N versions) 8
- (J versions) 9
- 4 REGISTER & MEMORY MAP 13
- 5 FLASH PROGRAM MEMORY 17
- 6 DATA EEPROM 18
- Interrupt enable 21
- Latch Access Transfer 21
- 8 CENTRAL PROCESSING UNIT 23
- Half carry 24
- Interrupt mask 24
- Negative 24
- Carry/borrow 24
- 00000001 25
- MAIN CLOCK 26
- CONTROLLER 26
- ■ an external source 30
- ■ an external RC oscillator 30
- LVD reset flag 32
- Clock security syst 32
- interrupt enable 32
- Watchdog reset flag 32
- 10 INTERRUPTS 33
- INTERRUPTS (Cont’d) 34
- Table 5. Interrupt mapping 34
- 11 POWER SAVING MODES 35
- 12 I/O PORTS 39
- Hardware Configuration 41
- OPEN-DRAIN OUTPUT 41
- PUSH-PULL OUTPUT 41
- Data register 8 bits 44
- Option register 8 bits 44
- I/O PORTS (Cont’d) 45
- 13 MISCELLANEOUS REGISTERS 46
- Main clock out selection 47
- CPU clock prescaler 47
- Slow mode select 47
- Must always be cleared 48
- Beep control 48
- SS mode selection 48
- SS internal mode 48
- 14 ON-CHIP PERIPHERALS 49
- Activation bit 50
- 7-bit timer (MSB to LSB) 50
- Watchdog flag 50
- WATCHDOG TIMER (Cont’d) 51
- Time base control 53
- Oscillator interrupt enable 53
- Oscillator interrupt flag 53
- clock speed) with the choice 54
- 16-BIT TIMER (Cont’d) 55
- Beginning of the sequence 56
- Sequence completed 56
- /CC[1:0]) 58
- 16-BIT FREE RUNNING 59
- OLVL2OLVL1 64
- Pulse Width Modulation cycle 65
- Input Capture Flag 1 69
- Output Compare Flag 1 69
- Timer Overflow Flag 69
- Input Capture Flag 2 69
- Output Compare Flag 2 69
- CAPTURE STROBE 77
- VR02131B 77
- Write Collision status 83
- Mode Fault flag 83
- TDRE TC RDRF IDLE OR NF FE 93
- R8 T8 - M WAKE - 94
- TIE TCIE RIE ILIE TE RE RWU 94
- First SCI Prescaler 95
- SCI Transmitter rate divisor 95
- SCI Receiver rate divisor 95
- 8-bit Extended Receive Pres 96
- 8-bit Extended Transmit Pres 96
- CH2 CH1CH3COCO 0 ADON 0 CH0 97
- ■ A/D conversion [duration: t 98
- D7 D6 D5 D4 D3 D2 D1 D0 99
- COCO 0 ADON 0 CH3 CH2 CH1 CH0 99
- 15 INSTRUCTION SET 101
- Relative (Indirect) 103
- INSTRUCTION GROUPS (Cont’d) 105
- 16 ELECTRICAL CHARACTERISTICS 107
- 16.6 MEMORY CHARACTERISTICS 122
- 16.6.2 EEPROM Data Memory 122
- 16.6.3 FLASH Program Memory 122
- R=10k~10MΩ 124
- UNUSED I/O PORT 128
- ADC Accuracy 139
- 17 PACKAGE CHARACTERISTICS 140
- ■ Heraeus: PD945, PD955 143
- ■ Loctite: 3615, 3298 143
- MICROCONTROLLER OPTION LIST 146
- DEVELOPMENT TOOLS (Cont’d) 148
- 18.4 ST7 APPLICATION NOTES 149
- 19 IMPORTANT NOTES 151
- 20 SUMMARY OF CHANGES 152
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