XC886/888CLM
Serial Interfaces
User’s Manual
12-34
V1.3, 2010-02
Serial Interfaces, V 1.0
TXD is the transmit line; the receive line is connected to its data input line RXD; the shift
clock line is either MS_CLK or SS_CLK. Only the device selected for master operation
generates and outputs the shift clock on line MS_CLK. Since all slaves receive this clock,
their pin SCLK must be switched to input mode. The external connections are
hard-wired, and the function and direction of these pins are determined by the master or
slave operation of the individual device.
Figure 12-13 SSC Full-Duplex Configuration
The data output pins MRST of all slave devices are connected together onto the single
receive line in the configuration shown in
. During a transfer, each slave
shifts out data from its shift register. There are two ways to avoid collisions on the receive
line due to different slave data:
•
Only one slave drives the line, i.e., enables the driver of its MRST pin. All the other
slaves must have their MRST pins programmed as input so only one slave can put
its data onto the master's receive line. Only the receiving of data from the master is
possible. The master selects the slave device from which it expects data either by
separate select lines, or by sending a special command to this slave. The selected
slave then switches its MRST line to output until it gets a de-selection signal or
command.
Master
Device #1
Shift Register
Clock
MTSR
MRST
CLK
CLK
MRST
MTSR
Transmit
Receive
Clock
Clock
Shift Register
Device #2
Slave
Slave
Device #3
MRST
CLK
MTSR
Clock
Shift Register
*
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