Measurement Computing DAC488 v.1 - Manual (Page 40)

34 DAC488 Operation DAC488 User’s Manual
Bus Commands
The following IEEE 488 bus commands are supported by DAC488:
•
Device Clear ( DCL ): Device Clear resets all devices, including the DAC488, to its power on state. The
DAC488 will be in the Listener Idle and Talker Idle state. The power on default settings for each
command will be programmed.
•
Group Execute Trigger ( GET ): When the DAC488 recognizes a GET , and the GET Trigger Mask ( G )
command has been used to arm the DAC488, it outputs the programmed voltage or voltage sequence
(depending on which mode the DAC488 is in) at the selected port(s).
•
My Listen Address ( MLA ): When the DAC488 is addressed to Listen, it accepts characters from the
Active Talker and interprets these characters as commands and command parameters.
•
My Talk Address ( MTA ): When the DAC488 is addressed to Talk, it returns a string specifying the
selected port along with the selected range and output voltage which was programmed for that port.
The DAC488 can also return a status string for each port or the entire interface by using the User Status
(
U ) command. Information about commands previously executed or data stored in the internal buffer
may be returned by using the Query ( ? ) command.
•
Selected Device Clear ( SDC ): Selected Device Clear resets a single device, in this case the DAC488, to
its power on state. The DAC488 will be in the Listener Idle and Talker Idle state. The power on
default settings for each command will be programmed.
•
Serial Poll Disable ( SPD ): Disables the DAC488 from responding to Serial Polls by the controller.
•
Serial Poll Enable ( SPE ): When Serial Poll Enabled, the DAC488 sets itself to respond to a Serial
Poll with its Serial Poll Status byte if addressed to Talk. When the Serial Poll byte is accepted by the
controller, any pending
SRQ s are cleared. The DAC488 will continue to try to output its Serial Poll
response until it is Serial Poll Disabled by the controller.
•
Unlisten ( UNL ): UNL places the DAC488 in the Listener Idle State.
•
Untalk ( UNT ): UNT places the DAC488 in the Talker Idle State.
Bus Addresses
The IEEE 488 interface standard permits up to 15 devices to be configured within one system. Each of
these devices must have a unique address to avoid confusion. In a similar fashion, every building in town
has a unique address to prevent one home from receiving another home's mail. Exactly how each device's
address is set is specific to the product's manufacturer. Some are set by DIP switches in hardware, others by
software. Consult the manufacturer's instructions to determine how to set the address.
Bus addresses are sent with bus (multiline) commands from the Active Controller. These commands
include My Listen Address (
MLA ), My Talk Address ( MTA ), Talk Address Group ( TAG ), and Listen Address
Group ( LAG ).
Bus Terminators
The terminating characters sent on output by the DAC488 are set by using the Bus Terminator ( Y )
command. Upon power on, the unit's IEEE 488 bus terminators are determined by the power-on
configuration saved using the System Defaults (
S ) command. The factory default terminator selection is CR
LF (carriage-return line-feed). The power on default terminators can be changed to any of the four available
options listed under the Bus Terminator ( Y ) command, described in Chapter 7. The four available
commands and the associated terminator options with them, are: (1) Y0 = CR LF , (2) Y1 = LF CR , (3) Y2
= CR only, and (4) Y3 = LF only. If it is desired to have particular power on default terminator(s), the
terminator(s) may be selected using the Bus Terminator command and then this selection may be saved
using the System Defaults (
S ) command.
The DAC488 ignores all terminators received from the bus controller. Only the Execute ( X ) command is
used to signal the DAC488 that a command string has been completed. The only exception to this rule is
the Trigger On (
@ ) command which is processed immediately upon receipt.