Measurement Computing WaveBook rev.3.0 - Manual (Page 140)

8-6 Theory of Operation, 6-24-99 WaveBook User’s Manual
During a “Read” from the Digital I/O Port
(WaveBook/512)
During a “Write” to the Digital I/O Port
(WaveBook/512)
The RD- signal is asserted for at least 225 ns. The WR- signal is asserted for at least 225 ns.
Within 10 ns after RD- is asserted, the address and enable lines are
valid. Within 10 ns after WR- is asserted, the address and enable lines are
valid.
The address and enable lines remain valid for a minimum of 0 ns
after RD- is unasserted. The address and enable lines remain valid for a minimum of 0 ns
after WR- is unasserted.
The data to be read must be presented to the D8-15 data lines within
185 ns after RD- is asserted and must be held until after RD- is
unasserted. The data [to be written] is driven on the D8-15 data lines at least
210 ns before WR- is unasserted and remains on the data lines until
after WR- is unasserted.
If the digital I/O port is used for both input and output, the data lines must not be driven for more
than 50 ns after RD- is unasserted.
If the digital I/O port is used only for input, then D8 - D15 may be driven indefinitely.
When read as the first element of a scan, the 8-bits that are read are left-justified within the 16-bit sample.
The remaining 8 bits are undefined and may appear as any value. Thus, a sample of the digital inputs is of
the form 00XXh to FFXXh where the left-most 8 bits are read from the port and the remaining bits
(shown as XX) are undefined.
When WaveBook is not acquiring data, then the daqIORead and daqIOWrite commands may be used
to read and write bytes at any one of the 32 addresses.
If the digital I/O port is only being used to sample the digital inputs during acquisitions, just connect the
digital signals to the digital I/O port data lines. If the digital I/O port is to be used for addressed I/O, using
the daqIORead and daqIOWrite commands, then the digital signals must conform to the timing
requirements shown in the digital I/O port-timing diagram shown below:
225 ns (min)
0 ns (min)
0 ns (min)
A0-4
EN-
D8-D15
(read)
10 ns (max)
v alid line
185 ns (max) 50 ns (max)
RD-
WR-
210 ns (min)
0 ns (min)
D8-D15
(write)
WaveBook/512, Digital I/O Port Timing