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ST72321xx-Auto I2C bus interface (I2C)
Doc ID 13829 Rev 1 167/243
16.7.3 I
2
C status register 2 (SR2)
1M/SL
Master/Slave
This bit is set by hardware as soon as the interface is in Master mode (writing
START = 1). It is cleared by hardware after detecting a Stop condition on the bus or
a loss of arbitration (ARLO = 1). It is also cleared when the interface is disabled
(PE = 0).
0: Slave mode
1: Master mode
0SB
Start bit (Master mode)
This bit is set by hardware as soon as the Start condition is generated (following a
write START = 1). An interrupt is generated if ITE = 1. It is cleared by software
reading SR1 register followed by writing the address byte in DR register. It is also
cleared by hardware when the interface is disabled (PE = 0).
0: No Start condition
1: Start condition generated
Table 84. SR1 register description (continued)
Bit Name Function
SR2 Reset value: 0000 0000 (00h)
76543210
Reserved AF STOPF ARLO BERR GCAL
- RORORORORO
Table 85. SR2 register description
Bit Name Function
7:5 - Reserved. Forced to 0 by hardware.
4AF
Acknowledge failure
This bit is set by hardware when no acknowledge is returned. An interrupt is
generated if ITE = 1. It is cleared by software reading SR2 register or by hardware
when the interface is disabled (PE = 0).
The SCL line is not held low while AF = 1 but by other flags (SB or BTF) that are set
at the same time.
0: No acknowledge failure
1: Acknowledge failure
Note: When an AF event occurs, the SCL line is not held low; however, the SDA line
can remain low if the last bits transmitted are all 0. It is then necessary to release
both lines by software.
3STOPF
Stop detection (Slave mode)
This bit is set by hardware when a Stop condition is detected on the bus after an
acknowledge (if ACK = 1). An interrupt is generated if ITE = 1. It is cleared by
software reading SR2 register or by hardware when the interface is disabled
(PE = 0).
The SCL line is not held low while STOPF = 1.
0: No Stop condition detected
1: Stop condition detected
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