15-12
MCF5249UM
MOTOROLA
Register Description and Programming
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 can still contain error detection and correction information.
One way to provide error 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.
15.3.5
BUS OPERATION
This section describes the operation of the bus during read, write, and interrupt- acknowledge cycles to the
UART module. All UART module registers must be accessed as bytes.
15.3.5.1
Read Cycles
The CPU accesses the UART module with 1 to 2 wait states because the core system clock is divided by 2
for the UART module. The UART module responds to reads with byte data on D[7:0]. Reserved registers
return logic zero during reads.
15.3.5.2
Write Cycles
The CPU with zero wait states accesses the UART module. The UART module accepts write data on
D[7:0]. Write cycles to read-only registers and reserved registers complete in a normal manner without
exception processing; however, the data is ignored.
15.3.5.3
Interrupt Acknowledge Cycles
The UART module can arbitrate for interrupt servicing and supply the interrupt vector when it has
successfully won arbitration. The vector number must be provided if interrupt servicing is necessary; thus,
the interrupt vector register (UIVR) must be initialized. The interrupt vector number generated by the IVR is
used if the autovector is not enabled in the SIM Interrupt Control Register (ICR). If the UIVR is not
initialized and the ICR is not programmed for autovector, a spurious interrupt exception is taken if
interrupts are generated. This works in conjunction with the MCF5249 interrupt controller, which allows a
programmable Interrupt Priority Level (IPL) for the interrupt.
15.4
REGISTER DESCRIPTION AND PROGRAMMING
This section contains a detailed description of each register and its specific function as well as flowcharts
of basic UART module programming.
15.4.1
REGISTER DESCRIPTION
Writing control bytes into the appropriate registers controls the UART operation. A list of UART module
registers and their associated addresses is shown in
Table 15-1.
Note: All UART module registers are accessible only as bytes. The contents of the mode
registers (UMR1 and UMR2), clock-select register (UCSR), and the auxiliary
control register (UACR) bit 7 should be changed only after the receiver/transmitter
is issued a software RESET command—i.e., channel operation must be disabled.
Be careful if the register contents are changed during receiver/transmitter
operations because unpredictable results can occur.
For the registers described in this section, the numbers above the register description represent the bit
position in the register. The register description contains the mnemonic for the bit. The values as shown in
the following tables are the values of those register bits after a hardware reset. A value of U indicates that
the bit value is unaffected by reset. The read/write status is shown in the last line.
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Freescale Semiconductor, Inc.
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