Agilent Technologies Agilent 34980A, User Manual

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328 34980A User’s Guide
13
Breadboard Module
Digital I/O Functions
The Digital input/output (DIO) interface provides two 8- bit bytes of DIO,
which may be accessed individually or combined together to form one
16- bit word. Three control lines are provided. See the Pin Connection
Information table (for P102) on
page 315 for connection information.
The three control lines provide handshake of the read/write SCPI
commands (
SENSe
and
SOURce
) sent to the mainframe, as follows:
Timing for Read Commands
When the 34980A receives a SCPI command to read from the breadboard,
control line 3 is set high (its default setting, indicating a read request).
If the read target is byte 1 , control line 1 is set strobe low, the byte 1
data is read, and then control line 1 is set strobe high. The strobe pulse
width is 3.75
3
s, and the time from strobe low to valid data is 1.25
3
s.
Similarly, if the read target is byte 2 , control line 2 is set strobe low, the
byte 2 data is read, and then control line 2 is set strobe high. The strobe
pulse width is 3.75
3
s, and the time from strobe low to valid data is
1.25
3
s.
If both bytes are configured as a word, and targeted as a word in the
read (
SENSe
) command , both control lines 1 and 2 are set strobe low,
all 16 bits are read, and then both control lines are set strobe high.
The strobe pulse width is longer (5
3
s) than for a single byte read, but the
time from strobe low to valid data is still 1.25
3
s.
In all three cases, once the data has been read by the mainframe, the data
lines are left in tri- state (indeterminate).
The read timing diagram is shown on page 329 .
Timing for Write Commands
When the 34980A receives a SCPI command to write to the breadboard,
control line 3 is set low (indicating a write request).
If the write target is byte 1 , control line 1 is set strobe low, the byte 1
data is written to the 8 output bits, and then control line 1 is set strobe
high. Valid data is present 1.25
3
s before the control line strobe is
set high. Control line 3 is then set high.
Similarly, if the write target is byte 2 , control line 2 is set strobe low, the
byte 2 data is written to the 8 output bits, and then control line 2 is set
strobe high. Valid data is present 1.25
3
s before the control line strobe is
set high. Control line 3 is then set high.