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Programming Model
13-16
ADSP-BF537 Blackfin Processor Hardware Reference
The
THRE
flag is set when
UARTx_THR
is ready for new data and cleared
when the processor loads new data into
UARTx_THR
. Writing
UARTx_THR
when it is not empty overwrites the register with the new value and the
previous character is never transmitted.
The
DR
flag signals when new data is available in
UARTx_RBR
. This flag is
cleared automatically when the processor reads from
UARTx_RBR
. Reading
UARTx_RBR
when it is not full returns the previously received value. When
UARTx_RBR
is not read in time, newly received data overwrites
UARTx_RBR
and the
OE
flag is set.
With interrupts disabled, these status flags can be polled to determine
when data is ready to move. Note that because polling is processor inten-
sive, it is not typically used in real-time signal processing environments.
Be careful if transmit and receive are served by different software threads,
because read operations on
UART_LSR
and
UART_IIR
registers are destruc-
tive. Polling the
SIC_ISR
register without enabling the interrupts by
SIC_MASK
is an alternate method of operation to consider. Software can
write up to two words into the
UARTx_THR
register before enabling the
UART clock. As soon as the
UCEN
bit is set, those two words are sent.
Alternatively, UART writes and reads can be accomplished by interrupt
service routines (ISRs). Separate interrupt lines are provided for UART
TX, UART RX, and UART error. The independent interrupts can be
enabled individually by the
UARTx_IER
register.
The ISRs can evaluate the status bit field within the
UARTx_IIR
register to
determine the signalling interrupt source. If more than one source is sig-
nalling, the status field displays the one with the highest priority.
Interrupts also must be assigned and unmasked by the processor’s inter-
rupt controller. The ISRs must clear the interrupt latches explicitly. See
.
Содержание Blackfin ADSP-BF537
Страница 42: ...Contents xlii ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 90: ...Development Tools 1 32 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 138: ...Programming Examples 4 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 340: ...SDC Programming Examples 6 84 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 606: ...Programming Examples 9 94 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 660: ...Programming Examples 10 54 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 720: ...Electrical Specifications 11 60 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 840: ...Programming Examples 13 42 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 876: ...Programming Examples 14 36 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 938: ...Programming Examples 15 62 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 958: ...Programming Examples 17 12 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 986: ...Programming Examples 18 28 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 1162: ...G 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 1218: ...Index I 56 ADSP BF537 Blackfin Processor Hardware Reference ...