M38512M4 Datasheet, PDF (30/61 Pages) Mitsubishi Electric Semiconductor – SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

MITSUBISHI MICROCOMPUTERS
3851 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
sPrecautions when using multi-master I² C-BUS
interface
(1) Read-modify-write instruction
The precautions when the read-modify-write instruction such as
SEB, CLB etc. is executed for each register of the multi-master
I²C-BUS interface are described below.
• I²C data shift register (S0: address 002B16)
When executing the read-modify-write instruction for this regis-
ter during transfer, data may become a value not intended.
• I²C address register (S0D: address 002C16)
When the read-modify-write instruction is executed for this regis-
ter at detecting the STOP condition, data may become a value
not intended. It is because H/W changes the read/write bit
(RBW) at the above timing.
• I²C status register (S1: address 002D16)
Do not execute the read-modify-write instruction for this register
because all bits of this register are changed by H/W.
• I²C control register (S1D: address 002E16)
When the read-modify-write instruction is executed for this regis-
ter at detecting the START condition or at completing the byte
transfer, data may become a value not intended. Because H/W
changes the bit counter (BC0-BC2) at the above timing.
• I²C clock control register (S2: address 002F16)
The read-modify-write instruction can be executed for this regis-
ter.
• I²C START/STOP condition control register (S2D: address
003016)
The read-modify-write instruction can be executed for this regis-
ter.
(2) START condition generating procedure using multi-master
1. Procedure example (The necessary conditions of the generat-
ing procedure are described as the following 2 to 5.
::
LDA —
(Taking out of slave address value)
SEI
(Interrupt disabled)
BBS 5, S1, BUSBUSY (BB flag confirming and branch pro-
cess)
BUSFREE:
STA S0
(Writing of slave address value)
LDM #$F0, S1
(Trigger of START condition generating)
CLI
(Interrupt enabled)
::
BUSBUSY:
CLI
(Interrupt enabled)
::
2. Use “Branch on Bit Set” of “BBS 5, $002D, –” for the BB flag
confirming and branch process.
3. Use “STA $2B, STX $2B” or “STY $2B” of the zero page ad-
dressing instruction for writing the slave address value to the
I²C data shift register.
4. Execute the branch instruction of above 2 and the store instruc-
tion of above 3 continuously shown the above procedure
example.
5. Disable interrupts during the following three process steps:
• BB flag confirming
• Writing of slave address value
• Trigger of START condition generating
When the condition of the BB flag is bus busy, enable interrupts
immediately.
(3) RESTART condition generating procedure
1. Procedure example (The necessary conditions of the generat-
ing procedure are described as the following 2 to 4.)
Execute the following procedure when the PIN bit is “0.”
::
LDM #$00, S1
(Select slave receive mode)
LDA —
(Taking out of slave address value)
SEI
(Interrupt disabled)
STA S0
(Writing of slave address value)
LDM #$F0, S1
(Trigger of RESTART condition generating)
CLI
(Interrupt enabled)
::
2. Select the slave receive mode when the PIN bit is “0.” Do not
write “1” to the PIN bit. Neither “0” nor “1” is specified for the
writing to the BB bit.
The TRX bit becomes “0” and the SDA pin is released.
3. The SCL pin is released by writing the slave address value to
the I²C data shift register.
4. Disable interrupts during the following two process steps:
• Writing of slave address value
• Trigger of RESTART condition generating
(4) Writing to I²C status register
Do not execute an instruction to set the PIN bit to “1” from “0” and
an instruction to set the MST and TRX bits to “0” from “1” simulta-
neously. It is because it may enter the state that the SCL pin is
released and the SDA pin is released after about one machine
cycle. Do not execute an instruction to set the MST and TRX bits
to “0” from “1” simultaneously when the PIN bit is “1.” It is because
it may become the same as above.
(5) Process of after STOP condition generating
Do not write data in the I²C data shift register S0 and the I²C sta-
tus register S1 until the bus busy flag BB becomes “0” after
generating the STOP condition in the master mode. It is because
the STOP condition waveform might not be normally generated.
Reading to the above registers do not have the problem.
30