Serial Communications (16C452)
Bit 4
This bit is the Break Interrupt (BI) indicator. Bit 4 is
set to logical 1 whenever the received data input is
held in the spacing (Logic 0) state for longer than a
full word transmission time (that is, the total time of
start bit + data bits + stop bits).
Note:
Bits 1 through 4 of the LSR are the error conditions
that produce a Receiver Line Status interrupt
whenever any of the corresponding conditions are
detected.
Bit 5
This bit is the Transmitter Holding Register Empty
(THRE) indicator. Bit 5 indicates that the 16C452 is
ready to accept a new character for transmission. In
addition, this bit causes the 16C452 to issue an
interrupt to the CPU when the THRE Interrupt
Enable is set high. The THRE bit is set to logical 1
when a character is transferred from the Transmitter
Holding register into the Transmitter Shift register.
The bit is reset to logical 0 concurrently with the
loading of the Transmitter Holding register by the
CPU.
Bit 6
This bit is the Transmitter Shift Register Empty
(TEMT) indicator. Bit 6 is set to logical 1 whenever
the Transmitter Shift register is idle. It is reset to
logical 0 upon a data transfer from the Transmitter
Holding register to the Transmitter Shift register and
remains low until the character is transferred out of
SOUT. Bit 6 is a read-only bit.
Bit 7
This bit is permanently set to logical 0.
8-27
Содержание ZT 8809A
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