
XBUS high-speed synchronous serial interface
UM0404
DocID13284 Rev 2
13.1 Full-duplex
operation
The different devices are connected through three lines. The definition of these lines is
always determined by the master: The line connected to the master's data output pin
MTSR1 is the transmit line, the receive line is connected to its data input line MRST1, and
the clock line is connected to pin SCLK1. Only the device selected for master operation
generates and outputs the serial clock on pin SCLK1. All slaves receive this clock, so their
pin SCLK1 must be switched to input mode (XDP6.5 = ‘0’). The output of the master’s shift
register is connected to the external transmit line, which in turn is connected to the slaves’
shift register input.
The output of the slaves’ shift register is connected to the external receive line in order to
enable the master to receive the data shifted out of the slave. The external connections are
hard-wired, the function and direction of these pins is determined by the master or slave
operation of the individual device.
Note:
applies for MSB-first operation as well
as for LSB-first operation.
When initializing the devices in this configuration, select one device for master operation
(SSCMS = ‘1’), all others must be programmed for slave operation (SSCMS = ‘0’).
Initialization includes the operating mode of the device's XSSC and also the function of the
respective port lines (see
Section 12.2.1: Port control on page 279
Figure 119. Serial clock phase and polarity options
Serial Clock
SCLK1
Transmit Data
Last
bit
Latch
Data
Shift Data
First
bit
Pins
MTSR1 / MRST1
SSCPO
SSCPH
0
0
1
1
0
1
0
1