FMS6501 Datasheet, PDF (8/16 Pages) Fairchild Semiconductor – 12 Input 9 Output Video Switch Matrix with Input Clamp, Input Bias Circuitry, and Output Drivers

Acknowledge
The number of data bytes transferred between the start
and stop conditions from transmitter to receiver is unlim-
ited. Each byte of eight bits is followed by an acknowl-
edge bit. The acknowledge bit is a HIGH level signal put
on the bus by the transmitter during which time the mas-
ter generates an extra acknowledge related clock pulse.
A slave receiver which is addressed must generate an
acknowledge after the reception of each byte. Also a
master receiver must generate an acknowledge after the
reception of each byte that has been clocked out of the
slave transmitter.
The device that acknowledges must pull down the SDA
line during the acknowledge clock pulse, so that the SDA
line is stable LOW during the HIGH period of the acknowl-
edge related clock pulse (set-up and hold times must be
taken into consideration). A master receiver must signal
an end of data to the transmitter by not generating an
acknowledge on the last byte that has been clocked out
of the slave. In this event the transmitter must leave the
data line HIGH to enable the master to generate a stop
condition.
START
condition
SCL FROM
MASTER
1
2
DATA OUTPUT
BY TRANSMITTER
DATA OUTPUT
BY RECEIVER
clock pulse for
acknowledgement
8
9
Figure 4: Acknowledgement on the I²C Bus
I²C Bus Protocol
Before any data is transmitted on the I²C bus, the device which should respond is addressed first. The addressing is always
carried out with the first byte transmitted after the start procedure. The I²C bus configuration for a data write to the FMS6501 is
shown below in figure 5:
1
91
9
SCL
SDA
START BY
MASTER
A6 A5 A4 A3 A2 A1 A0 R/W
D7
FRAME1
SERIAL BUS ADDRESS BYTE
ACK. BY
FMS6501
D6 D5 D4 D3 D2 D1 D0
07
ACK. BY
FRAME 2
FMS6501
ADDRESS POINTER REGISTER BYTE
1
9
SCL(CONTINUED)
SDA(CONTINUED)
D7 D6 D5 D4 D3 D2 D1 D0
FRAME 3
DATA BYTE
ACK. BY _{STOP BY}
FMS6501 _MASTER
Figure 5: Write a register address to the pointer register, then write data to the selected register
FMS6501 Rev. 1A
8
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