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UART Modules
32-25
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discarded if the received A/D bit is 0 (data tag). If the receiver is enabled, all received characters are
transferred to the CPU through the receiver holding register during read operations.
In either case, data bits load into the data portion of the FIFO while the A/D bit loads into the status portion
of the FIFO normally used for a parity error (USR
n
[PE]).
Framing error, overrun error, and break detection operate normally. The A/D bit takes the place of the
parity bit; therefore, parity is neither calculated nor checked. Messages in this mode may continues
containing error detection and correction information. If 8-bit characters are not required, one way to
provide error detection is to use software to calculate parity and append it to the 5-, 6-, or 7-bit character.
32.4.5
Bus Operation
This section describes bus operation during read, write, and interrupt acknowledge cycles to the UART
module.
32.4.5.1
Read Cycles
The UART module responds to reads with byte data. Reserved registers return zeros.
32.4.5.2
Write Cycles
The UART module accepts write data as bytes only. Write cycles to read-only or reserved registers
complete normally without an error termination, but data is ignored.
32.5
Initialization/Application Information
The software flowchart,
, consists of:
•
UART module initialization—These routines consist of SINIT and CHCHK (See Sheet 1 p. 32-28
and Sheet 2 p. 32-29). Before SINIT is called at system initialization, the calling routine allocates
2 words on the system FIFO. On return to the calling routine, SINIT passes UART status data on
the FIFO. If SINIT finds no errors, the transmitter and receiver are enabled. SINIT calls CHCHK
to perform the checks. When called, SINIT places the UART in local loopback mode and checks
for the following errors:
— Transmitter never ready
— Receiver never ready
— Parity error
— Incorrect character received
•
I/O driver routine—This routine (See Sheet 4 p. 32-31 and Sheet 5 p. 32-32) consists of INCH, the
terminal input character routine which gets a character from the receiver, and OUTCH, which
sends a character to the transmitter.
•
Interrupt handling—This consists of SIRQ (See Sheet 4 p. 32-31), which is executed after the
UART module generates an interrupt caused by a change-in-break (beginning of a break). SIRQ
then clears the interrupt source, waits for the next change-in-break interrupt (end of break), clears
the interrupt source again, then returns from exception processing to the system monitor.
Содержание MCF54455
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