Measurement Computing DAC488 v.1 - Manual (Page 44)

38 IEEE 488 Background DAC488 User’s Manual
Bus Command Groups
Bus (multiline) commands are bytes sent by the Active Controller over the data bus with Attention ( ATN )
asserted. These commands are sent to all devices and are divided into the following 5 groups:
•
Addressed Command Group ( ACG ): These commands affect only those devices which have previously
been addressed to be a Listener. There are 5 bus line addressed commands: GET , GTL , PPD , SDC , and
TCT .
•
Universal Command Group ( UCG ): These commands cause every instrument on the bus to carry out
the bus function specified (if the instrument is capable of it). There are 5 bus line universal commands:
DCL , LLO , PPU , SPD , and SPE .
•
Listen Address Group ( LAG ): These commands address to Listen specified bus devices. There are 31
(0 to 30) Listen addresses associated with this group. The 3 most significant bits of the data bus are set
to
001 while the 5 least significant bits are the address of the device being told to Listen.
•
Talk Address Group ( TAG ): These commands address to Talk specified bus devices. There are 31 (0
to 30) Talk addresses associated with this group. The 3 most significant bits of the data bus are set to
010 while the 5 least significant bits are the address of the device being told to Talk.
•
Secondary Command Group ( SCG ): These commands are used to specify a subaddress or subfunction
within a given bus device. These are any one of the 32 possible commands (0 to 31) in this group.
They must immediately follow a Talk or Listen address.
•
Three bus commands not found in the above 5 groups are: MLA , MTA , and PPC .
All of the IEEE 488 bus commands are further described individually, as follows:
•
Device Clear ( DCL ): This command causes all bus devices to be initialized to a pre-defined or power
up state.
•
Group Execute Trigger ( GET ): This command usually signals a group of devices to begin executing a
triggered action. This allows actions of different devices to begin simultaneously.
•
Go To Local ( GTL ): This command allows the selected devices to be manually controlled.
•
Local Lock Out ( LLO ): This command prevents manual control of the instrument's functions.
•
My Listen Address ( MLA ): This command addresses a device to Listen. The device accepts data from
the Active Talker and outputs this data through the serial interface. It substitutes the selected serial
terminators for the received IEEE 488 bus terminators.
•
My Talk Address ( MTA ): This command addresses a device to Talk. The device retrieves data from
the serial input buffer and outputs it to the IEEE 488 bus. It substitutes the selected IEEE 488 bus
terminators for the received serial terminators. The device will continue to output serial input buffer
data as long as the IEEE 488 controller allows.
•
Parallel Poll Configure ( PPC ): This command configures devices capable of performing a Parallel
Poll via the data bit they are to assert in response to a Parallel Poll.
•
Parallel Poll Disable ( PPD ): This command disables the Parallel Poll response of selected devices.
•
Parallel Poll Unconfigure ( PPU ): This disables all devices from responding to a Parallel Poll.
•
Selected Device Clear ( SDC ): This command causes a single device to be initialized to a pre-defined or
power up state.