25
3851 Group
(Built-in 16 KB ROM)
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
MITSUBISHI MICROCOMPUTERS
Fig. 25 Interrupt request signal generating timing
Fig. 24 Structure of I
2
C status register
•Bit 6: Communication mode specification bit (transfer direc-
tion specification bit: TRX)
This bit decides a direction of transfer for data communication.
When this bit is “0,” the reception mode is selected and the data of
a transmitting device is received. When the bit is “1,” the transmis-
sion mode is selected and address data and control data are
output onto the SDA in synchronization with the clock generated
on the SCL.
This bit is set/reset by software and hardware. About set/reset by
hardware is described below. This bit is set to “1” by hardware
when all the following conditions are satisfied:
• When ALS is “0”
• In the slave reception mode or the slave transmission mode
• When the R/W bit reception is “1”
This bit is set to “0” in one of the following conditions:
• When arbitration lost is detected.
• When a STOP condition is detected.
• When writing “1” to this bit by software is invalid by the START
condition duplication preventing function (Note).
• With MST = “0” and when a START condition is detected.
• With MST = “0” and when ACK non-return is detected.
• At reset
•Bit 7: Communication mode specification bit (master/slave
specification bit: MST)
This bit is used for master/slave specification for data communica-
tion. When this bit is “0,” the slave is specified, so that a START
condition and a STOP condition generated by the master are re-
ceived, and data communication is performed in synchronization
with the clock generated by the master. When this bit is “1,” the
master is specified and a START condition and a STOP condition
are generated. Additionally, the clocks required for data communi-
cation are generated on the SCL.
This bit is set to “0” in one of the following conditions.
• Immediately after completion of 1-byte data transfer when arbi-
tration lost is detected
• When a STOP condition is detected.
• Writing “1” to this bit by software is invalid by the START condi-
tion duplication preventing function (Note).
• At reset
Note: START condition duplication preventing function
The MST, TRX, and BB bits is set to “1” at the same time after con-
firming that the BB flag is “0” in the procedure of a START condition
occurrence. However, when a START condition by another master
device occurs and the BB flag is set to “1” immediately after the con-
tents of the BB flag is confirmed, the START condition duplication
preventing function makes the writing to the MST and TRX bits in-
valid. The duplication preventing function becomes valid from the
rising of the BB flag to reception completion of slave address.
SCL
PIN
IICIRQ
b7
MST
b0
I
2
C status register
(S1 : address 002D
16
)
Last receive bit (Note)
0 : Last bit = “0”
1 : Last bit = “1”
General call detecting flag
(Note)
0 : No general call detected
1 : General call detected
Slave address comparison flag
(Note)
0 : Address disagreement
1 : Address agreement
Arbitration lost detecting flag
(Note)
0 : Not detected
1 : Detected
SCL pin low hold bit
0 : SCL pin low hold
1 : SCL pin low release
Bus busy flag
0 : Bus free
1 : Bus busy
Communication mode
specification bits
00 : Slave receive mode
01 : Slave transmit mode
10 : Master receive mode
11 : Master transmit mode
TRX BB PIN AL AAS AD0 LRB
Note: These bits and flags can be read out, but cannot
be written.
Write “0” to these bits at writing.
(88 paginas)
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