Motorola MCF5281 사용자 설명서

23-28

MOTOROLA

 

detection, if 8-bit characters are not required, is to use software to calculate parity and
append it to the 5-, 6-, or 7-bit character.

This section describes bus operation during read, write, and interrupt acknowledge cycles
to the UART module.

The UART module responds to reads with byte data. Reserved registers return zeros.

The UART module accepts write data as bytes. Write cycles to read-only or reserved
registers complete normally without exception processing, but data is ignored.

The software flowchart, Figure 23-26, consists of the following:

• UART module initialization—These routines consist of SINIT and CHCHK (sheets 

1 and 2). Before SINIT is called at system initialization, the calling routine allocates 
2 words on the system stack. On return to the calling routine, SINIT passes UART 
status data on the stack. 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 loop-back mode and checks for the following errors:
— Transmitter never ready
— Receiver never ready
— Parity error
— Incorrect character received

• I/O driver routine—This routine (sheets 4 and 5) 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—Consists of SIRQ (sheet 4), 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.