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 3s, and the time from strobe low to valid data is 1.25 3s.
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 3s, and the time from strobe low to valid data is
1.25 3s.
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 3s) than for a single byte read, but the
time from strobe low to valid data is still 1.25 3s.
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 3s 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 3s before the control line strobe is
set high. Control line 3 is then set high.
To Next Page
Loading...
Need help?
General
