NEC uPD78056Y User Manual
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CHAPTER 17 SERIAL INTERFACE CHANNEL 0 (
µ
PD78054Y Subseries)
(4) Various signals
A list of signals in the I
2
C bus mode is given in Table 17-4.
Table 17-4. Signals in I
2
C Bus Mode
Signal name
Description
Start condition
Definition :
SDA0 (SDA1) falling edge when SCL is high
Note 1
Function :
Indicates that serial communication starts and subsequent data are address data.
Signaled by :
Master
Signaled when :
CMDT is set.
Affected flag(s) :
CMDD (is set.)
Stop condition
Definition :
SDA0 (SDA1) rising edge when SCL is high
Note 1
Function :
Indicates end of serial transmission.
Signaled by :
Master
Signaled when :
RELT is set.
Affected flag(s) :
RELD (is set) and CMDD (is cleared)
Acknowledge signal (ACK)
Definition :
Low level of SDA0(SDA1) pin during one SCL clock cycle after serial reception
Function :
Indicates completion of reception of 1 byte.
Signaled by :
Master or slave
Signaled when :
ACKT is set with ACKE = 1.
Affected flag(s) :
ACKD (is set.)
Wait (WAIT)
Definition :
Low-level signal output to SCL
Function :
Indicates state in which serial reception is not possible.
Signaled by :
Slave
Signaled when :
WAT1, WAT0 = 1x.
Affected flag(s) :
None
Serial Clock (SCL)
Definition :
Synchronization clock for output of various signals
Function :
Serial communication synchronization signal.
Signaled by :
Master
Signaled when :
See Note 2 below.
Affected flag(s) :
CSIIF0. Also see Note 3 below.
Address (A6 to A0)
Definition :
7-bit data synchronized with SCL immediately after start condition signal
Function :
Indicates address value for specification of slave on serial bus.
Signaled by :
Master
Signaled when :
See Note 2 below.
Affected flag(s) :
CSIIF0. Also see Note 3 below.
Transfer direction (R/W)
Definition :
1-bit data output in synchronization with SCL after address output
Function :
Indicates whether data transmission or reception is to be performed.
Signaled by :
Master
Signaled when :
See Note 2 below.
Affected flag(s) :
CSIIF0. Also see Note 3 below.
Data (D7 to D0)
Definition :
8-bit data synchronized with SCL, not immediately after start condition
Function :
Contains data actually to be sent.
Signaled by :
Master or slave
Signaled when :
See Note 2 below.
Affected flag(s) :
CSIIF0. Also see Note 3 below.
Notes 1. The level of the serial clock can be controlled by CLC of interrupt timing specify register (SINT).
2. Execution of instruction to write data to SIO0 when CSIE0 = 1 (serial transfer start directive). In the
wait state, the serial transfer operation will be started after the wait state is released.
3. If the 8-clock wait is selected when WUP = 0, CSIIF0 is set at the rising edge of the 8th clock cycle
of SCL. If the 9-clock wait is selected when WUP = 0, CSIIF0 is set at the rising edge of the 9th clock
cycle of SCL. CSIIF0 is set if an address is received and that address coincides with the value of
the slave address register (SVA) when WUP = 1, or if the stop condition is detected.