8. Offset Adjust
Offsets and bias currents at the integrator input can cause an
additional positional offset at the output of the converter of
1 arc minute typical, 5.3 arc minutes maximum. If this can be
tolerated, then R8 and R9 can be omitted from the circuit.
If fitted, the following values of R8 and R9 should be used:
R8 = 4.7 MΩ, R9 = 1 MΩ potentiometer
To adjust the zero offset, ensure the resolver is disconnected
and all the external components are fitted. Connect the COS
pin to the REFERENCE INPUT and the SIN pin to the
SIGNAL GROUND and with the power and reference ap-
plied, adjust the potentiometer to give all “0s” on the digital
The potentiometer may be replaced with select on test resistors
To transfer data the INHIBIT input should be used. The data
will be valid 490 ns after the application of a logic “LO” to the
INHIBIT. This is regardless of the time when the INHIBIT is
applied and allows time for an active BUSY to clear. By using
the ENABLE input the two bytes of data can be transferred
after which the INHIBIT should be returned to a logic “HI”
state to enable the output latches to be updated.
The validity of the output data is indicated by the state of the
BUSY output. When the input to the converter is changing, the
signal appearing on the BUSY output is a series of pulses at
TTL level. A BUSY pulse is initiated each time the input moves
by the analog equivalent of one LSB and the internal counter is
incremented or decremented.
The INHIBIT logic input only inhibits the data transfer from
the up-down counter to the output latches and, therefore, does
not interrupt the operation of the tracking loop. Releasing the
INHIBIT automatically generates a BUSY pulse to refresh the
The ENABLE input determines the state of the output data. A
logic “HI” maintains the output data pins in the high imped-
ance condition, and the application of a logic “LO” presents the
data in the latches to the output pins. The operation of the
ENABLE has no effect on the conversion process.
BYTE SELECT Input
The BYTE SELECT input selects the byte of the position data
to be presented at the data output DB1 to DB8. The least sig-
nificant byte will be presented on data output DB9 to DB16
(with the ENABLE input taken to a logic “LO”) regardless of
the state of the BYTE SELECT pin. Note that when the
AD2S83 is used with a resolution less than 16 bits the unused
data lines are pulled to a logic “LO.” A logic “HI” on the BYTE
SELECT input will present the eight most significant data bits
on data output DB1 and DB8. A logic “LO” will present the
least significant byte on data outputs 1 to 8, i.e., data outputs
1 to 8 will duplicate data outputs 9 to 16.
The operation of the BYTE SELECT has no effect on the con-
version process of the converter.
As the output of the converter passes through the major carry,
i.e., all “1s” to all “0s” or the converse, a positive going edge on
the RIPPLE CLOCK (RC) output is initiated indicating that a
revolution, or a pitch, of the input has been completed.
The minimum pulsewidth of the ripple clock is 300 ns. RIPPLE
CLOCK is normally set high before a BUSY pulse and resets
before the next positive going edge of the next BUSY pulse.
The only exception to this is when DIR changes while the
RIPPLE CLOCK is high. Resetting of the RIPPLE clock will
only occur if the DIR remains stable for two consecutive posi-
tive BUSY pulse edges.
If the AD2S83 is being used in a pitch and revolution counting
application, the ripple and busy will need to be gated to prevent
false decrement or increment (see Figure 2).
RIPPLE CLOCK is unaffected by INHIBIT.
NOTE: DO NOT USE ABOVE CCT WHEN INHIBIT IS LOW.
Figure 2. Diode Transistor Logic Nand Gate