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Example 3: Write data into the transmit buffer of channel A.
mov dx,base ; load base address
out dx,al ; write data in ax to buffer
Example 4: Read data from the receive buffer of channel A.
mov dx,base ; load base address
in al,dx ; write data in ax to buffer
Table 2 SCC read register description.
External/Status interrupt information RR15
Upper byte of baud rate time constantRR13
Lower byte of baud rate time constantRR12
Miscellaneous status parameters RR10
Receive buffer RR8
MSB of frame byte count and FIFO status registerRR7
LSB of frame byte count register RR6
Interrupt Pending bits RR3
Modified Channel B interrupt vector and Unmodified Channel A
interrupt vector
RR2
Special Receive Condition status, residue codes, error conditions RR1
Transmit, Receive buffer statuses and external status RR0
The SCC can perform three basic forms of I/O operations: polling, interrupts, and
block transfer. Polling transfers data, without interrupts, by reading the status of
RR0 and then reading or writing data to the SCC buffers via CPU port accesses.
Interrupts on the SCC can be sourced from the receiver, the transmitter, or
External/Status conditions. At the event of an interrupt, Status can be determined,
then data can be written to or read from the SCC via CPU port accesses. For
block transfer mode, DMA transfers accomplish data transfers from the SCC to
memory or from memory to the SCC, interrupting the CPU only when the Block
is finished. Further information on these subjects are found in the chapters titled
INTERRUPTS, and DIRECT MEMORY ACCESS.
The SCC incorporates additional circuitry supporting serial communications. This
circuitry includes clocking options, baud rate generator (BRG), data encoding, and
internal loopback. The SCC may be programmed to select one of several sources
to provide the transmit and receive clocks. These clocks can be programmed in
WR11 to come from the RTXC pin, the TRXC pin, the output of the BRG, or the
transmit output of the DPLL. The MPA-200 uses the TRXC pin for its transmit
7 Quatech Inc., MPA-200/300 Manual