mcf5272 Freescale Semiconductor, Inc, mcf5272 Datasheet - Page 390

• Manufacturer Part Number: mcf5272
• Description: Mcf5272 Coldfire Integrated Microprocessor User
• Manufacturer: Freescale Semiconductor, Inc

Operation
A character sent from the master station consists of a start bit, a programmed number of
data bits, an address/data (A/D) bit flag, and a programmed number of stop bits. A/D = 1
indicates an address character; A/D = 0 indicates a data character. The polarity of A/D is
selected through UMR1n[PT]. UMR1n should be programmed before enabling the
transmitter and loading the corresponding data bits into the transmit buffer.
In multidrop mode, the receiver continuously monitors the received data stream, regardless
of whether it is enabled or disabled. If the receiver is disabled, it sets the RxRDY bit and
loads the character into the receiver holding register FIFO stack provided the received A/D
bit is a one (address tag). The character is discarded if the received A/D bit is zero (data
tag). If the receiver is enabled, all received characters are transferred to the CPU through
the receiver holding register stack during read operations.
In either case, the data bits are loaded into the data portion of the stack while the A/D bit is
loaded into the status portion of the stack normally used for a parity error (USRn[PE]).
Detection of breaks and framing or overrun errors operates normally. The A/D bit replaces
the parity bit, so parity is neither calculated nor checked. Messages in this mode may still
contain error detection and correction information. If 8-bit characters are not required,
software can be used to calculate parity and append it to the 5-, 6-, or 7-bit character.
16-30
USRn[RxRDY]
USRn[TxRDY]
Transmitter
Receiver
Enabled
Enabled
internal
module
internal
module
select
select
RxD
TxD
UMR1n[PM] = 11
UMR1n[PT] = 1
UMR1n
UMR1n[PM] = 11
Figure 16-30. Multidrop Mode Timing Diagram
[PM] = 11
A/D
ADD 1
0
UMR1n[PT] = 0
ADD1
ADD1
A/D
A/D
C0
MCF5272 User’s Manual
1
1
ADD 1
Peripheral Station
C0
C0
Master Station
A/D
A/D
Status Data
UMR1n[PT] = 2
(C0)
ADD 2
ADD2
ADD2
A/D
A/D
1
1
Status Data
(ADD 2)
A/D
MOTOROLA
0