STV3550 datasheet(99/144 Pages) STMICROELECTRONICS

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STV3550

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The connections between the SSC2 ports and the relevant PIO pads are shown in Figure 63.

The pad control block inside the SSC2 determines which of the serial_data_in ports is used to read

data from (depending on the master or slave mode). It also determines which of the serial_data_out

ports to write data to (depending on the master or slave mode).

The deselected serial_data_out port is driven to ground (except in I²C mode when it is driven high).

Therefore the user must ensure that the relevant PIO pad output enable is turned off depending on

the master/slave status of the SSC.

It is up to the user to ensure that the PIO pads are configured correctly for direction and output

driver type (e.g. push/pull or open drain).

Throughout the rest of this document the data in and out ports will be referred to as

“serial_data_out” and “serial_data_in”, where this is assumed to be the correct pair of pins

dependent on the master or slave mode of the SSC2.

7.7.4

Clock Generation

If the SSC2 is configured to be the bus master, then it will generate a serial clock signal on the

serial_clock_out port.

The clock signal can be controlled for polarity and phase and its period (baud rate) can be set to a

variety of frequencies.

For I²C operation there are also a number of additional clocking features. These are described in

Section 7.7.16: I²C Operation.

7.7.5

Clock Control

In master mode, the serial clock, SCL, is generated by the SSC2 according to the setting of the

phase, SSCPH, and polarity, SSCPO bits in the control register.

The polarity bit, SSCPO, defines the logic level the clock idles at i.e. when the SSC2 is in master

mode, but is between transactions. A polarity bit of 1 indicates an idle level of logic 1, 0 indicates

idle of logic 0.

Figure 63: PIO Pad Connections To SSC2

serial_clock_in

serial_clock_out

serial_data_in

alt_data_out<Y>

alt_data_out<X>

data_from_pads<Y>

data_from_pads<X>

SCL

SDA

output_enable<Y>

output_enable<X>

PIO

serial_data_out

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