Measurement-computing Serial488A Manual de usuario descargar pdf (Pagina 50)

4.1

Peripheral Operation

4.1 Peripheral Mode Operation

This mode of operation is useful in interfacing a serial device, such as a serial

printer, plotter or instrument, to an IEEE controller. Data which is sent by the IEEE

controller to the

Serial488A

is buffered and transmitted out its serial port. Data

received from the serial device is buffered by the

Serial488A

until read by the IEEE

controller. The

Serial488A

and the

Serial488A/OEM

can buffer approximately

32,000 bytes of data from both the IEEE input and the serial input. The

Serial488/512K

can buffer 512,000 bytes of data from both the IEEE input and the

serial input.

The

Serial488A

will refuse to accept more data from the IEEE controller when

its buffer memory is full. It does this by preventing completion of the bus

handshaking sequences. It will also request that additional serial data not be sent by

negating its Request To Send (

RTS

) output or by transmitting the

Xoff

ASCII

character. The serial handshake used is dependent on the handshake selection (Refer

Section 2

4.2 Serial and IEEE Input Buffers

Memory in the

Serial488A

is dynamically allocated for the serial input and

IEEE input buffers. This allows for the most efficient partitioning of memory for any

given application.

At power on, or device clear, each buffer is allocated a 128 byte mini-buffer or

queue. When the serial input [or IEEE input] requires more buffer space, additional

queues are allocated. When a queue is empty, it is released from the input buffers so

that it may be re-allocated when, and where, required.

There are approximately 250 available queues in the

Serial488A

and the

Serial488A/OEM

for a total of 32,000 bytes of buffer (character) space. Queues are

continually allocated and released as required by the serial and IEEE input. Of the 250

available queues, 240 are issued without regard to controlling the receipt of additional

serial or IEEE input data.

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