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L4450A 64-Bit Digital I/O with Memory and Counter 8
L4400 User’s Guide 205
Synchronous Handshake Mode
In the synchronous handshake mode, a strobe or clock signal is used to
transfer data to or from an external device. The strobe line (H1) is an output
and is pulsed once for each transfer.
Synchronous Unbuffered Inputs For synchronous handshake unbuffered inputs
the H0 line indicates the direction of the transfer. This line is set high to
indicate an input operation. The H0 line will remain in the high state until the
L4450A direction is changed. The H1 line is the strobe output line. The H2 line
is not used and is set to high impedance.
The timing of the input operation is controlled by the T
CYCLE
parameter set
using the
CONFigure:DIGital:HANDshake:RATE command. This setting
affects strobe width, memory clock rate, as well as the setup and hold times.
Alternatively, the reciprocal form of the command
CONFigure:DIGital:HANDshake:CTIMe can be used to specify the speed in
terms of time instead of a rate. T
CYCLE
begins when the L4450A executes one
of the input commands.
The timing should be set such that the device sending the data ensures the
data lines are valid prior to T
SETUP
time. The trailing edge of the strobe line
indicates the L4450A will latch the data within the T
HOLD
time. T
SETUP
is 90 ns
and T
HOLD
is 0 ns. Since T
HOLD
= 0 ns, the sending device can use the trailing
edge of the strobe to initiate a change in the data lines.
A synchronous unbuffered input is shown in the diagram below
(default handshake line polarity).
For example, the following SCPI commands set the L4450A to have a 16- bit
input using synchronous handshake. Two data inputs are then performed and
the strobe line is pulsed for each query. The I/O direction line is set high
following the first
SENSe:DIGital:DATA:WORD? query and remains high until
the digital channel is reset or reconfigured.
CONF:DIG:WIDT WORD, (@1101)
CONF:DIG:DIR INP, (@1101)
CONF:DIG:HAND SYNC, (@1101)
SENS:DIG:DATA:WORD? (@1101)
SENS:DIG:DATA:WORD? (@1101)
H0 (Direction)
H1 (Strobe)
Data In
Don't-Care Valid Don't-Care
T
SETUP
T
HOLD
T
CYCLE
T
CYCLE
/ 2 T
CYCLE
/ 2