Measurement Computing Digital488/80A - Manual (Page 61)

Data received for output to the digital ports must be contained within a
D command prefix and a Z terminator suffix. If
the amount of data sent is less than the number of bits programmed as outputs, then the least-significant bits contain
the data sent and the most-significant bits are cleared to logic 0. If the data sent is greater than the number of bits
programmed for output or selected by the Port Select (
P ) command, then the Digital488/80A generates a Conflict Error
( E3 ) and ignores the entire command string up to the next Execute ( X ) command. The Data Strobe output is pulsed
for approximately 50 microseconds after new data is output on the selected port(s).
When the Digital488/80A is addressed to Talk in Data Ready (
R ) mode R0 , it asserts Inhibit, reads the data from all 5
ports, unasserts Inhibit, and outputs the number of characters determined by the Bus Input/Output ( G ) and Port Select
( P ) commands. Leading zeros are not suppressed, and the bus terminators are appended to the output. After output,
the Digital488/80A must be readdressed to Talk to perform subsequent reads. In Data Ready ( R ) mode R1 or R2 ,
EDR may also be used to capture data in this data format.
Data Format
F4 - Binary
In Data Format F4 , no error checking is performed, and caution must be exercised when using this mode to avoid
locking the IEEE 488 bus.
When addressed to Listen, the Digital488/80A expects the
D command prefix, followed by 5 bytes of data beginning
with PORT5 without the Z terminator suffix. If any digital I/O port is configured as an input, then the data to that input
port is ignored.
When the Digital488/80A is addressed to Talk in Data Ready (
R ) mode R0 , it asserts Inhibit, reads the data from all 5
ports, unasserts Inhibit, and outputs 5 bytes beginning with PORT5 with EOI asserted on the last byte. Bus
terminators, with the exception of EOI , are not appended to the output. After output, the Digital488/80A must be
readdressed to Talk to perform subsequent reads. In Data Ready ( R ) mode R1 or R2 , EDR may also be used to
capture data in this data format.
Data Format
F5 - High-Speed Binary
In Data Format F5 , the command interpreter is disabled. When addressed to Listen, the Digital488/80A treats all bytes
received as data to be output to the digital I/O ports. Each time it receives 5 bytes or detects EOI asserted, it pulses
the Data Strobe for approximately 15 microseconds. Data is expected in a PORT5, PORT4, PORT3, PORT2, PORT1
sequence. If only 2 bytes are received, with
EOI asserted on the second byte, then the Digital488/80A updates
PORT5 with the first byte received, PORT4 with the second byte received, and pulses the Data Strobe. Since all
received characters are treated as data, no commands are recognized.
To place the Digital488/80A in format
F5 , the 3-character string F5X should be the last command sent to the interface
without terminators. Any characters appended to this command, such as the carriage return ( CR ) or line feed ( LF ), are
considered data and the output ports reflects those character values.
When the Digital488/80A is addressed to Talk in Data Ready (
R ) mode R0 , it asserts Inhibit, reads the data from all 5
ports, unasserts Inhibit, and outputs the binary data to the bus with EOI asserted on the fifth byte. When the last data
byte is transferred, the data is read again in anticipation of another data transfer. If Inhibit is used to sequence external
hardware, this line pulses N+1 times, where N is the number of total 5-byte data transfers. In this format, the
Digital488/80A does not have to be readdressed to Talk to read the ports multiple times. EDR cannot be used to
capture data in this data format.
The only programmable method to exit Data Format
F5 , is Device Clear ( DCL ) or Selected Device Clear ( SDC ). When
either channel or both channels are in format F5 , a DCL or an SDC to either channel clears format F5 , by enabling the
command interpreter and changing the format to F0 (default ASCII hexadecimal). A DCL or an SDC does not reset the
Digital488/80A; it only takes the unit out of format F5 and places it into format F0 . All other parameters remain
unchanged. In addition, the Clear output line is not pulsed by DCL or SDC when the Digital488/80A is in format F5 .
CAUTION
Because the Configuration (C) command is used, the following programming
example(s) will not work properly if the HVCX1 option is installed with a conflicting
hardware configuration. To be safe, remove the HVCX1 board and replace it with the
jumper board to run the example(s).
EXAMPLE 1: Data Format F0 - ASCII Hexadecimal. (See next page.)
Digital488/80A User’s Manual 967695 Digital488/80A Commands 55