FS7140, FS7145
http://onsemi.com
8
SYNC Circuitry
The FS7145 supports nearly instantaneous adjustment of
the output CLK phase by the SYNC input. Either edge
direction of SYNC (positive−going or negative−going) is
supported.
Example (positive−going SYNC selected): Upon the
negative edge of SYNC input, a sequence begins to stop the
CLK output. Upon the positive edge, CLK resumes
operation, synchronized to the phase of the SYNC input
(plus a deterministic delay). This is performed by control of
the device post−divider. Phase resolution equal to 1/2 of the
VCO period can be achieved (approximately down to 2 ns).
I
2
C−bus Control Interface
This device is a read/write slave device meeting all Philips
I
2
C−bus specifications except a ”general call.” The bus has
to be controlled by a master device that generates the serial
clock SCL, controls bus access and generates the START
and STOP conditions while the device works as a slave. Both
master and slave can operate as a transmitter or receiver, but
the master device determines which mode is activated. A
device that sends data onto the bus is defined as the
transmitter, and a device receiving data as the receiver.
I
2
C−bus logic levels noted herein are based on a
percentage of the power supply (V
DD
). A logic−one
corresponds to a nominal voltage of V
DD
, while a logic−zero
corresponds to ground (V
SS
).
Bus Conditions
Data transfer on the bus can only be initiated when the bus
is not busy. During the data transfer, the data line (SDA)
must remain stable whenever the clock line (SCL) is high.
Changes in the data line while the clock line is high will be
interpreted by the device as a START or STOP condition.
The following bus conditions are defined by the I
2
C−bus
protocol.
Not Busy
Both the data (SDA) and clock (SCL) lines remain high to
indicate the bus is not busy.
START Data Transfer
A high to low transition of the SDA line while the SCL
input is high indicates a START condition. All commands to
the device must be preceded by a START condition.
STOP Data Transfer
A low to high transition of the SDA line while SCL input
is high indicates a STOP condition. All commands to the
device must be followed by a STOP condition.
Data Valid
The state of the SDA line represents valid data if the SDA
line is stable for the duration of the high period of the SCL
line after a START condition occurs. The data on the SDA
line must be changed only during the low period of the SCL
signal. There is one clock pulse per data bit.
Each data transfer is initiated by a START condition and
terminated with a STOP condition. The number of data bytes
transferred between START and STOP conditions is
determined by the master device, and can continue
indefinitely. However, data that is overwritten to the device
after the first eight bytes will overflow into the first register,
then the second, and so on, in a first−in, first−overwritten
fashion.
Acknowledge
When addressed, the receiving device is required to
generate an acknowledge after each byte is received. The
master device must generate an extra clock pulse to coincide
with the acknowledge bit. The acknowledging device must
pull the SDA line low during the high period of the master
acknowledge clock pulse. Setup and hold times must be
taken into account.
The master must signal an end of data to the slave by not
generating and acknowledge bit on the last byte that has been
read (clocked) out of the slave. In this case, the slave must
leave the SDA line high to enable the master to generate a
STOP condition.
I
2
C−bus Operation
All programmable registers can be accessed randomly or
sequentially via this bi−directional two wire digital
interface. The crystal oscillator does not have to run for
communication to occur.
The device accepts the following I
2
C−bus commands:
Slave Address
After generating a START condition, the bus master
broadcasts a seven−bit slave address followed by a R/W bit.
The address of the device is:
A6 A5 A4 A3 A2 A1 A0
1 0 1 1 0 X X
where X is controlled by the logic level at the ADDR pins.
The selectable ADDR bits allow four different FS7140
devices to exist on the same bus. Note that every device on
an I
2
C−bus must have a unique address to avoid possible bus
conflicts.
Random Register Write Procedure
Random write operations allow the master to directly
write to any register. To initiate a write procedure, the R/W
bit that is transmitted after the seven−bit device address is a
logic−low. This indicates to the addressed slave device that
a register address will follow after the slave device
acknowledges its device address. The register address is
written into the slave’s address pointer. Following an
acknowledge by the slave, the master is allowed to write
eight bits of data into the addressed register. A final
acknowledge is returned by the device, and the master
generates a STOP condition.
