9

RUN/HOLD (PIN 4)

When high (or open) the A/D will free-run with equally

spaced measurement cycles every 40,0002 /4,002 clock

pulses. If taken low, the converter will continue the full

measurement cycle that it is doing and then hold this reading

as long as Pin 4 is held low. A short positive pulse (greater

then 300ns) will now initiate a new measurement cycle

beginning with up to 10,001 /1,001 counts of auto zero. Of

course if the pulse occurs before the full measurement cycle

(40,002 /4,002 counts) is completed, it will not be recognized

and the converter will simply complete the measurement it is

doing. An external indication that full measurement cycle

has been completed is that the first STROBE pulse (see

below) will occur 101 / 11 counts after the end of this cycle.

Thus, if RUN/HOLD is low and has been low for at least

101 / 11 counts, converter is holding and ready to start a new

measurement when pulsed high.

STROBE (PIN 18)

This is a negative-going output pulse that aids in transferring

the BCD data to external latches, UARTs or

microprocessors. There are 5 negative-going STROBE

pulses that occur once and only once for each measurement

cycle starting 101 /11 pulses after the end of the full

measurement cycle. Digit 5 (MSD) goes high at the end of

the measurement cycle and stays on for 201 / 21 counts. In

the center of this digit pulse (to avoid race conditions

between changing BCD and digit drives) the first STROBE

Digit 5, Digit 4 goes high (for 200 / 20 clock pulses) and

100 / 10 pulses later the STROBE goes negative for the

second time. This continues through Digit 1 (LSD) when the

fifth and last STROBE pulse is sent. The digit drive will

continue to scan (unless the previous signal was over-range)

but no additional STROBE pulses will be sent until a new

measurement is available.

BUSY (PIN 28)

BUSY goes high at the beginning of signal integrate and

stays high until the first clock pulse after zero-crossing (or

after end of measurement in the case of an OVER-RANGE).

The internal latches are enabled (i.e., loaded) during the first

clock pulse after BUSY and are latched at the end of this

clock pulse. The circuit automatically reverts to auto-zero

when not BUSY so it may also be considered an A-Z signal.

A very simple means for transmitting the data down a single

wire pair from a remote location would be to AND BUSY with

clock and subtract 10,001 /1,001 counts from the number of

pulses received - as mentioned previously there is one “NO-

count” pulse in each Reference Integrate cycle.

OVER-RANGE (PIN 4)

This pin goes positive when the input signal exceeds the

range (20,000 /2,000) of the converter. The output F-F is set

at the end of BUSY and is reset to zero at the beginning of

Reference Integrate in the next measurement cycle.

UNDER-RANGE (PIN 13)

This pin goes positive when the reading is 9% of range or

less. The output F-F is set at the end of BUSY (if the new

reading is 1800 /180 or less) and is reset a the beginning of

Signal Integrate of the next reading.

POLARITY (PIN 3)

This pin is positive for a positive input signal. It is valid even for a

zero reading. In other words, +0000 means the signal is

positive but less than the least significant bit. The converter can

be used as null detector by forcing equal (+) and (-) readings.

The null at this point should be less than 0.1 LSB. This output

becomes valid at the beginning of Reference Integrate and

remains correct until it is revalidated for the next measurement.

DIGIT DRIVES (PINS 19, 24, 25, 26, AND 27)

Each digit drive is a positive-going signal which lasts for

unless and OVER-RANGE occurs. Then all Digit drives are

blanked from the end of the STROBE sequence until the

the scan again. This gives a blinking display as a visual

indication of OVER-RANGE.

BCD (PINS 20, 21, 22 AND 23)

logic signals that go on simultaneously with the Digit driver.

ICL8052A/ICL71C03, ICL8068A/ICL71C03