IEEE 488.1 Requirements for High-Speed Operation (T1 Delay
≥
350 ns)
The IEEE 488.1 standard requires that devices used in high-speed operation must use three-
state, 48 mA drivers on most signals. Each device must add no more than 50 pF capacitance
on each signal, and all devices must be powered on.
The total cable length in a system must be no more than 15 m, or 1 m times the number of
devices in the system.
HS488 System Requirements
An HS488 system must meet the IEEE 488.1 requirements and it must implement the
following three new interface functions:
•
Talking devices must use the
Source Handshake Extended (SHE)
interface function,
which is an extension of the IEEE 488.1 SH function.
•
Listening devices must use the
Acceptor Handshake Extended (AHE)
interface function,
which is an extension of the IEEE 488.1 AH function. Accepting devices must have a
buffer of at least 3 bytes to store received data.
•
HS488 devices must implement the
Configuration (CF)
interface function. At system
power on, the Controller uses previously undefined multiline messages to configure
HS488 devices. The CF function enables devices to interpret these multiline messages.
Sequence of Events in Data Transfers
The following figure shows a typical IEEE 488.1 data transfer.
Figure 15. IEEE 488.1 Transfers
~DIO18
(composite)
~DAV
~NFRD
~NDAC
IEEE 488.1 Three-Wire Transfers
The following figure shows an HS488 data transfer. The HS488 protocol modifies the IEEE
488.1 SH and AH functions. At the beginning of each data transfer, the HS488 SHE and AHE
functions determine whether all active Talkers and Listeners are capable of HS488 transfers. If
the addressed devices are HS488-capable, they use the HS488 noninterlocked handshake
protocol for that data transfer. If any addressed device is not HS488-capable, the transfer
continues using the standard three-wire handshake.
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GPIB-140B User Manual