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10
Data Device Corporation
www.ddc-web.com
RD-19240
Pre 1-1-04/05-0
INHIBIT, ENABLE, AND CB TIMING
The Inhibit (INH) signal is used to freeze the digital output angle
in the transparent output data latch while data is being trans-
ferred. Application of an inhibit signal does not interfere with the
continuous tracking of the converter. As shown in FIGURE 10,
angular output data is valid 150 ns maximum after the applica-
tion of the negative inhibit pulse.
Output angle data is enabled onto the tri-state data bus in two
bytes. Enable MSBs (EM) is used for the most significant 8 bits
and Enable LSBs (EL) is used for the least significant 6 bits. As
shown in FIGURE 11, output data is valid 150 ns maximum after
the application of a negative enable pulse. The tri-state data bus
returns to the high impedance state 100 ns maximum after the
rising edge of the enable signal.
The Converter Busy (CB) signal indicates that the tracking con-
verter output angle is changing 1 LSB. As shown in FIGURE 12,
output data is valid 50 ns maximum after the middle of the CB
pulse. The CB pulse width is 1/40 Fs, which is nominally 375 ns.
Note that the INH signal may be applied regardless of the logic
state of the CB signal. If an INH signal is applied and the CB line is
busy, the INH will wait for CB to finish before setting the INH latch.
BUILT-IN-TEST (BIT)
The BIT output is active low, and is triggered if any of the follow-
ing conditions exist:
1) Loss of Signal (LOS) - Sin and Cos inputs both less than
500mV.
2) Loss of Reference (LOR) - Reference Input less than 500 mV.
3) Excessive Error - This error is detected by monitoring the
demodulator output, which is proportional to the difference
between the analog input and digital output. When it exceeds
approximately 100 LSBs (in the selected resolution), BIT will
be asserted. This condition can occur any time the analog
input changes at a rate in excess of the maximum tracking
rate. During power up, the converter may see a large differ-
ence between the sin/cos inputs and the digital output angle
held in its counter. BIT will be asserted until the converter set-
tles within ~ 100 LSB’s of the final result.
4) 180° phase error input signal to reference input (false null)
causes a BIT plus kickstarts the converter counter to correct
the error.
A 500 s dynamic delay occurs before the error BIT becomes
active. This dynamic delay is responsive to the active filter
loop.
;;
;;;
DATA
VALID
150 ns max
INHIBIT
100 ns MAX
ENABLE
150 ns MAX
DATA
VALID
HIGH Z
For 16 bit bus, EM and EL may be tied to ground for transparent mode,
providing only one 16 bit R/D channel is on the data bus.
1/40 FS
(375 nsec nominal)
CB
50 ns
DATA
VALID
DATA
VALID
*
* Next CB pulse
cannot occur for
a minimum of
150 nsec.
FIGURE 10. INHIBIT TIMING
FIGURE 11. ENABLE TIMING
FIGURE 12. CONVERTER BUSY TIMING