Renesas PCA7429G02 Informacje Techniczne Strona 43

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SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER with CLOSED CAPTION DECODER
and ON-SCREEN DISPLAY CONTROLLER
M37272M6/M8–XXXSP/FP, M37272MA–XXXSP
M37272E8SP/FP, M37272EFSP
MITSUBISHI MICROCOMPUTERS
Rev. 1.3
Fig. 8.6.12 Address Data Communication Format
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8.6.12 Precautions when using multi-master
I
2
C-BUS interface
(1) Read-modify-write instruction
The precautions when the raead-modify-write instruction such as SEB,
CLB etc. is executed for each register of the multi-master I
2
C-BUS
interface are described below.
•I
2
C data shift register (S0)
When executing the read-modify-write instruction for this register
during transfer, data may become a value not intended.
•I
2
C address register (S0D)
When the read-modify-write instruction is executed for this register
at detecting the STOP condition, data may become a value not
intended. It is because hardware changes the read/write bit (RBW)
at the above timing.
•I
2
C status register (S1)
Do not execute the read-modify-write instruction for this register
because all bits of this register are changed by hardware.
•I
2
C control register (S1D)
When the read-modify-write instruction is executed for this register
at detecting the START condition or at completing the byte transfer,
data may become a value not intended. Because hardware changes
the bit counter (BC0–BC2) at the above timing.
•I
2
C clock control register (S2)
The read-modify-write instruction can be executed for this register.
(2) START condition generating procedure us-
ing multi-master
Procedure example (The necessary conditions of the generating
procedure are described as the following to ).
LDA (Taking out of slave address value)
SEI (Interrupt disabled)
BBS 5,S1,BUSBUSY
(BB flag confirming and branch process)
BUSFREE:
STA S0 (Writing of slave address value)
LDM #$F0, S1
(Trigger of START condition generating)
CLI (Interrupt enabled)
BUSBUSY:
CLI (Interrupt enabled)
Use “STA,” “STX” or “STY” of the zero page addressing instruction
for writing the slave address value to the I
2
C data shift register.
Use “LDM” instruction for setting trigger of START condition gener-
ating.
Write the slave address value of above and set trigger of START
condition generating of above continuously shown the above
procedure example.
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.
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