MPC555 / MPC556
TPU ROM FUNCTIONS
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
D-47
D.19 Serial Input/Output Port (SIOP)
The serial input/output port (SIOP) TPU function uses two or three TPU channels to
form a uni- or bi-directional synchronous serial port that can be used to communicate
with a wide variety of devices. Features such as baud rate and transfer size are user
programmable. The function can also produce a clock-only, when it uses just one
channel.
The SIOP TPU function has been designed to closely resemble the SIOP hardware
port found on some Motorola MCUs and can be used to add serial capabilities to a de-
vice without a serial port, or extend the capabilities of one with a hardware synchro-
nous port.
SIOP operates in master mode (i.e., the TPU always generates the clock) and the fol-
lowing features are programmable:
1. Choice of clock-only (one channel), clock + transmit (two channels), clock + re-
ceive (two channels) or clock + tr receive (three channels) operating
modes
2. Baud rate period is freely programmable over a 15-bit range of TCR1 counts
3. Selection of msb or lsb first shift direction
4. Variable transfer size from one to 16 bits
5. Clock polarity is programmable
When a transfer of data is complete the SIOP function notifies the host CPU by issuing
an interrupt request. The arrangement of the multiple SIOP channels is fixed: the data
out channel is the channel above the clock channel and the data in channel is the
channel below the clock channel. In clock-only or uni-directional mode, the unused
TPU channels are free to run other TPU functions. Two possible SIOP configurations
are show in
Figure D-29 Two Possible SIOP Configurations
Da ta Out-Chan x+1
Clo c k Out-Chan x
Da ta In-Cha n x-1
7
6
5
4
3
2
1
0
7
6
5
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3
2
1
0
Da ta Out-Cha n x+1
Cloc k Out-Chan
x
7
6
5
4
3
2
1
0
8
9
8-bit bi-directional transfer, MSB first with data valid on clock rising edge
10-bit output only transfer, LSB first with data valid on clock falling edge
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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