AC37 High-Speed Communication Adapter Card
REGISTER DEFINITION
LINE STATUS REGISTER:
OFFSET 5 - READ ONLY
This register can be read to obtain the current status of the receive or transmit buffers. The function of each bit is
described below:
Bit 0:
Receive Data Available
When the AC37 is operating in mode 0*, this bit will be set to a logic 1 whenever the
receive FIFO has data in it. When the AC37 is operating in mode 1*, this bit will be held
to a logic 0 until the last character of a Remote I/O command response is put into the
receive buffer. Bit 0 can be reset to a logic 0 by either reading all the data from the
receive buffer or by resetting the FIFO. The receive FIFO is 512 bytes deep.
* Refer to the section on Modes of Operation for a more detailed explanation of the different operating modes.
Bit 1:
Overrun Error Indicator
This bit is set to a logic 1 whenever the CPU of the AC37 attempts to put data into the
receive FIFO while it is full. When this occurs, the data currently in the FIFO is unaf-
fected but the incoming data is lost. The receive FIFO is 512 bytes deep. The Overrun
Error Indicator is reset to a logic 0 when the Line Status Register is read.
Bit 2:
Not Used
This bit is not used and will always read as a logic 0.
Bit 3:
Framing Error, Overrun Error, Parity Error Indicator
This bit is set only when the the CPU of the AC37 experiences a framing error, overrun
error, or parity error while receiving data. This bit is cleared when the Line Status
Register is read.
Bit 4:
Not Used
This bit is not used and will always read as a logic 0.
Bit 5:
Transmit Buffer Empty
Bit 5 is set whenever the transmit FIFO is ready to accept data. The transmit FIFO is 512
bytes deep. When the transmit FIFO becomes full, this bit is set to a logic zero. It will
remain set to a logic zero until enough data has been transmitted to cause the FIFO to
only be half full.
Bit 6:
Transmit Driver Active
This bit is set to a logic 0 while the AC37 is transmitting data. This bit is set to a logic 1
when the AC37 is not transmitting and is ready to receive data.
Bit 7:
Not Used
This bit is not used and will always read as a logic 0.
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