the µP, in that data can be accessed independently of

the clock. The output latches are normally updated on

the rising edge of

BUSY. But if CS and RD are low

when

BUSY goes high, the data latches are not updat-

ed until one of these inputs returns high. Additionally,

the MX7576 stops converting and

BUSY stays high until

RD or CS goes high. This mode of operation allows a

simple interface to the µP.

Processor Interface for Signal Acquisition (MX7575)

In many applications, it is necessary to sample the

input signal at exactly equal intervals to minimize errors

due to sampling uncertainty or jitter. In order to achieve

this objective with the previously discussed interfaces,

the user must match software delays or count the num-

ber of elapsed clock cycles. This becomes difficult in

interrupt-driven systems where the uncertainty in inter-

rupt servicing delays is another complicating factor.

The solution is to use a real-time clock to control the

start of a conversion. This should be synchronous with

the CLK input to the ADC (both should be derived from

the same source), because the sampling instants occur

three clock cycles after

CS and RD go low. Therefore,

the sampling instants occur at exactly equal intervals if

the conversions are started at equal intervals. In this

scheme, the output data is fed into a FIFO latch, which

allows the µP to access data at its own rate. This guar-

antees that data is not read from the ADC in the middle

of a conversion. If data is read from the ADC during a

conversion, the conversion in progress may be dis-

turbed, but the accessed data that belonged to the pre-

vious conversion will be correct.

The track/hold starts holding the input on the third

falling edge of the clock after

CS and RD go low. If CS

and

RD go low within 20ns of a falling clock edge, the

ADC may or may not consider this falling edge as the

first of the three edges that determine the sampling

instant. Therefore, the

CS and RD should not be

allowed to go low within this period when sampling

accuracy is required.

CMOS, µP-Compatible, 5µs/10µs, 8-Bit ADCs

_______________________________________________________________________________________

7

Figure 7. MX7575/MX7576 to Z-80 ROM Interface

ADDRESS

DECODE

ADDRESS BUS

+5V

DATA BUS

Z-80

MREQ

RD

RD

CS

EN

TP/MODE

D7

D0

DB7

DB0

MX7575*

MX7576

* SOME CIRCUITRY OMITTED FOR CLARITY

Figure 8. MX7575/MX7576 to TMS32010 ROM Interface

ADDRESS

DECODE

ADDRESS BUS

+5V

DATA BUS

PA2

PA0

MEN

DEN

RD

CS

EN

TP/MODE

D7

D0

DB7

DB0

MX7575*

MX7576

TMS32010

* SOME CIRCUITRY OMITTED FOR CLARITY

Figure 9. MX7576 Asynchronous Conversion Mode Timing

Diagram

CS

RD

BUSY

DATA

HIGH-

IMPEDANCE

BUS

HIGH-

IMPEDANCE

BUS

VALID

DATA

HIGH-IMPEDANCE BUS

VALID

DATA

UPDATE

LATCH

DEFER

UPDATING

ADDRESS

ENCODE

ADDRESS BUS

DATA BUS

ADDRESS

LATCH

8085A

A0–A15

RD

RD

CS

MODE

D0–D7

ALE

AD0–AD7

MX7576*

* SOME CIRCUITRY OMITTED FOR CLARITY

Figure 10. MX7576 to 8085A Asynchronous Conversion Mode

Interface