# Read and Write Termination

The IEEE 488 specification defines two methods of identifying the last byte of device-dependent (data) messages. The two methods permit a talker to send data messages of any length without the listener(s) knowing in advance the number of bytes in the transmission. The two methods are as follows:

- END message—The talker asserts the End Or Identify (EOI) signal simultaneously with the transmission of the last data byte. By design, the listener stops reading when it detects a data message accompanied by EOI, regardless of the value of the byte.

- End of String (EOS) character—The talker uses a special character at the end of its data string. You can configure the listener to stop receiving data when it detects that character. You can use either a 7-bit ASCII character or a full 8-bit binary byte.

You can use these methods individually or in combination. However, you must properly configure the listener to unambiguously detect the end of a transmission.

Using the ibconfig function, you can accommodate all permissible forms of read and write termination. You can change the default configuration settings for read and write termination at run time using ibeos and ibeot. In accordance with the IEEE 488 specification, you cannot force the handler to ignore END on read operations.