SYNCHRONOUS SERIAL INTERFACE (SSI)
6 - 100
PORT C
MOTOROLA
6.4.2.3.12
SSI Transmit Data Register (TX)
TX is a 24-bit write-only register. Data to be transmitted is written into this register and is
automatically transferred to the transmit shift register. The data written (8, 12, 16, or 24
bits) should occupy the most significant portion of TX (see Figure 6-48). The unused bits
(least significant portion) of TX are don’t care bits. The DSP is interrupted whenever TX
becomes empty if the transmit data register empty interrupt has been enabled.
6.4.2.3.13
Time Slot Register (TSR)
TSR is effectively a null data register that is used when the data is not to be transmitted
in the available transmit time slot. For the purposes of timing, TSR is a write-only register
that behaves like an alternative transmit data register, except that, rather than transmitting
data, the transmit data pin is in the high-impedance state for that time slot.
6.4.3
Operational Modes and Pin Definitions
Table 6-12 and Table 6-13 completely describe the SSI operational modes and pin definitions
(Table 6-5 is a simplified version of these tables). The operational modes are as follows:
1. Continuous Clock
Mode 1 – Normal with Internal Frame Sync
Mode 2 – Network with Internal Frame Sync
Mode 3 – Normal with External Frame Sync
Mode 4 – Network with External Frame Sync
2. Gated Clock
Mode 5 – External Gated Clock
Mode 6 – Normal with Internal Gated Clock
Mode 7 – Network with Internal Gated Clock
3. Special Case (Both Gated and Continuous Clock)
Mode 8 – On-Demand Mode (Transmitter Only)
Mode 9 – Receiver Follows Transmitter Clocking
6.4.4
Registers After Reset
Hardware or software reset clears the port control register bits, which configure all I/O as
general-purpose input. The SSI will remain in reset while all SSI pins are programmed as
general-purpose I/O (CC8–CC3=0) and will become active only when at least one of the
SSI I/O pins is programmed as not general-purpose I/O. Table 6-14 shows how each type
of reset affects each SSI register bit.
F
re
e
sc
a
le
S
e
m
ic
o
n
d
u
c
to
r,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
c
.
..