SDA3302 Datasheet, PDF (3/27 Pages) Siemens Semiconductor Group – GHz PLL with I2C Bus and Four Chip Addresses

SDA 3302 Family
Circuit Description (cont’d)
P0-P2
P4-P7
CAS
The software-switched outputs (P0, P1, P2) can be used for direct band
selection (20-mA current output).
P4, P5, P6 and P7 are open-collector outputs for a variety of different
purposes. The test bit T1 = 1 switches the test signals f _REF (4 MHz/512) and
Cy (divided input signal) to P6 and P7.
Four different chip addresses can be set by appropriate connection of pin
CAS.
I²C-Bus Interface
SCL, SDA
Data are exchanged between the processor and the PLL on the I²C bus. The
clock is produced by the processor (input SCL), while pin SDA works as an
input or output depending on the direction of the data (open collector;
external pullup resistor). Both inputs have hysteresis and a lowpass
characteristic, which enhances the noise immunity of the I²C bus.
The data from the processor are applied to an I²C bus controller and filed in
registers according to their function. When the bus is free, both lines are in
the marking state (SDA, SCL are high). Each telegram begins with a start
condition and ends with the stop condition. Start condition: SDA goes low
while SCL remains high; stop condition: SDA goes high while SCL remains
high. All further data exchanges occur while SCL is low and are accepted by
the controller with the positive clock edge.
For what follows, refer to the table of logic allocations.
All telegrams are transmitted byte by byte, followed by a ninth clock pulse,
during which the controller puts the SDA line on low (acknowledge condition).
The first byte consists of seven address bits, with which the processor
selects the PLL from a number of peripheral devices (chip select). The eighth
bit is always low. In the data portion of the telegram the first bit of the first or
third data byte determines whether a divider ratio or control information
follows. In each case the byte following the first byte must be of the same
data type (or a stop condition).
V_S, GND
When the supply voltage is applied, a power-on reset circuit prevents the PLL
from putting the SDA line on low, which would block the bus.
Semiconductor Group
3