National Instruments GPIB-BUF EOI

Chapter 3 Technical Information

DMA Controller transfers the data directly to the internal data buffer

without processor intervention. Thus, GPIB transfer rates as high as 900

kbytes/s are possible. The GPIB-BUF turns off the EMPTY indicator as

soon as it starts receiving data from the host.

The buffered data is then sent to the target device connected to the GPIB

OUT port at the maximum acceptance rate of the target device. The GPIB

OUT port is interrupt-driven and is asynchronous with respect to any DMA

activity that is taking place on the GPIB IN port. Both events take place

concurrently and without user intervention.

If very large amounts of data are sent to the GPIB-BUF (greater than the

amount of RAM in the system) and the target device is a very slow data

acceptor (such as a printer or plotter), the internal data buffer of the

GPIB-BUF can become full. If this happens, the FULL indicator on the

front panel illuminates. This is not an error condition, but an indication that

the GPIB transfer rate from the GPIB Talker to the GPIB-BUF has slowed

to approximately the same rate as that of the target device accepting the

data.

Upon being addressed to talk, the GPIB-BUF updates the front panel

address indicators by turning on the TALK indicator and turning off the

LISTEN indicator. The GPIB-BUF waits for all the data in its internal

buffer to be accepted by the target, and then addresses the target device to

talk. Any data sent from the target device to the GPIB-BUF is not buffered,

but is passed directly through the GPIB-BUF to the GPIB IN port. Since no

buffer space is required when the GPIB-BUF is addressed to talk, all the

RAM in the system can be dedicated to providing the largest possible buffer

space for data coming into the GPIB IN port.

EOI

The GPIB End Or Identify (EOI) signal is used by the GPIB Listener(s) to

determine when the GPIB Talker has finished sending data. Without it, the

GPIB Listener must either know in advance the exact amount of data that

the Talker will send or must know of some terminating character sequence

that the Talker will adhere to when sending data. EOI signal reception and

transmission is fully supported on the GPIB-BUF.

When sending data while addressed as a GPIB Talker, the GPIB-BUF

asserts EOI* on the GPIB IN port with any byte received from the target

device that has the EOI* signal line asserted.