Queued Serial Multi-Channel Module
MPC561/MPC563 Reference Manual, Rev. 1.2
Freescale Semiconductor
15-55
When TE is cleared, the transmitter is disabled after all pending idle, data, and break frames are
transmitted. The TC flag is set, and control of the TXD pin reverts to PQSPAR and DDRQS. Buffered data
is not transmitted after TE is cleared. To avoid losing data in the buffer, do not clear TE until TDRE is set.
Some serial communication systems require a mark on the TXD pin even when the transmitter is disabled.
Configure the TXD pin as an output, then write a one to either QDTX1 or QDTX2 of the PORTQS register.
See
Section 15.5.1, “Port QS Data Register (PORTQS)
.” When the transmitter releases control of the TXD
pin, it reverts to driving a logic one output.
To insert a delimiter between two messages, to place non-listening receivers in wake-up mode between
transmissions, or to signal a re-transmission by forcing an idle-line, clear and then set TE before data in
the serial shifter has shifted out. The transmitter finishes the transmission, then sends a preamble. After the
preamble is transmitted, if TDRE is set, the transmitter marks idle. Otherwise, normal transmission of the
next sequence begins.
Both TDRE and TC have associated interrupts. The interrupts are enabled by the transmit interrupt enable
(TIE) and transmission complete interrupt enable (TCIE) bits in SCCxR1. Service routines can load the
last data frame in a sequence into SCxDR, then terminate the transmission when a TDRE interrupt occurs.
Two SCI messages can be separated with minimum idle time by using a preamble of 10 bit-times (11 if a
9-bit data format is specified) of marks (logic ones). Follow these steps:
1. Write the last data frame of the first message to the TDRx
2. Wait for TDRE to go high, indicating that the last data frame is transferred to the transmit serial
shifter
3. Clear TE and then set TE back to one. This queues the preamble to follow the stop bit of the current
transmission immediately.
4. Write the first data frame of the second message to register TDRx
In this sequence, if the first data frame of the second message is not transferred to TDRx prior to the finish
of the preamble transmission, then the transmit data line (TXDx pin) marks idle (logic one) until TDRx is
written. In addition, if the last data frame of the first message finishes shifting out (including the stop bit)
and TE is clear, TC goes high and transmission is considered complete. The TXDx pin reverts to being a
general-purpose output pin.
15.7.7.6
Receiver Operation
The receiver can be divided into two segments. The first is the receiver bit processor logic that
synchronizes to the asynchronous receive data and evaluates the logic sense of each bit in the serial stream.
The second receiver segment controls the functional operation and the interface to the CPU including the
conversion of the serial data stream to parallel access by the CPU.
15.7.7.7
Receiver Bit Processor
The receiver bit processor contains logic to synchronize the bit-time of the incoming data and to evaluate
the logic sense of each bit. To accomplish this an RT clock, which is 16 times the baud rate, is used to
sample each bit. Each bit-time can thus be divided into 16 time periods called RT1–RT16. The receiver
Summary of Contents for MPC561
Page 84: ...MPC561 MPC563 Reference Manual Rev 1 2 lxxxiv Freescale Semiconductor...
Page 144: ...Signal Descriptions MPC561 MPC563 Reference Manual Rev 1 2 2 46 Freescale Semiconductor...
Page 206: ...Central Processing Unit MPC561 MPC563 Reference Manual Rev 1 2 3 62 Freescale Semiconductor...
Page 302: ...Reset MPC561 MPC563 Reference Manual Rev 1 2 7 14 Freescale Semiconductor...
Page 854: ...Time Processor Unit 3 MPC561 MPC563 Reference Manual Rev 1 2 19 24 Freescale Semiconductor...
Page 968: ...Development Support MPC561 MPC563 Reference Manual Rev 1 2 23 54 Freescale Semiconductor...
Page 1144: ...Internal Memory Map MPC561 MPC563 Reference Manual Rev 1 2 B 34 Freescale Semiconductor...
Page 1212: ...TPU3 ROM Functions MPC561 MPC563 Reference Manual Rev 1 2 D 60 Freescale Semiconductor...
Page 1216: ...Memory Access Timing MPC561 MPC563 Reference Manual Rev 1 2 E 4 Freescale Semiconductor...