AD7824/AD7828
–10–
REV. F
MICROPROCESSOR INTERFACING
The AD7824/AD7828 is designed to interface to microprocessors
as Read Only Memory (ROM). Analog channel selection, con-
version start, and data read operations are controlled by CS, RD,
and the channel address inputs. These signals are common to
all memory peripheral devices.
Z80 MICROPROCESSOR
Figure 16 shows a typical AD7824/AD7828–Z80 interface. The
AD7824/AD7828 is operating in Mode 0. Assume the ADC is
assigned a memory block starting at address C000. The follow-
ing LOAD instruction to any of the addresses listed in Table II
will start a conversion of the selected channel and read the
conversion result.
LD B, (C000)
At the beginning of the instruction cycle when the ADC
address is selected, RDY asserts the WAIT input so that the
Z80 is forced into a WAIT state. At the end of conversion,
RDY returns high and the conversion result is placed in the B
register of the microprocessor.
DATA BUS
ADDRESS BUS
ADDRESS
DECODE
EN
5V
5k⍀
A0
A1
A2
Z80
AD7824*
AD7828*
A15
A0
MREQ
WAIT
RD
D7
D0
CS
RDY
RD
DB7
DB0
A0 A1 A2**
LINEAR CIRCUITRY OMITTED FOR CLARITY.
FOR THE AD7828 ONLY
**
*
Figure 16. AD7824/AD7828–Z80 lnterface
Table II. Address Channel Selection
AD7824 AD7828
Address Channel Channel
C000 1 1
C001 2 2
C002 3 3
C003 4 4
C004 5
C005 6
C006 7
C007 8
MC68000 MICROPROCESSOR
Figure 17 shows an MC68000 interface. The AD7824/AD7828
is operating in Mode 0. Assume the ADC is again assigned a
memory block starting at address C000. A MOVE instruction
to any of the addresses in Table II starts a conversion and reads
the conversion result.
MOVE × B $C000, D0
Once conversion has begun, the MC68000 inserts WAIT states
until INT goes low, asserting DTACK at the end of conversion.
The microprocessor then places the conversion results into the
D0 register.
DATA BUS
ADDRESS BUS
ADDRESS
DECODE
EN
5V
5k⍀
A0
A1
A2
AD7824*
AD7828*
A23
A1
D7
D0
CS
RDY
RD
DB7
DB0
A0 A1 A2**
CLR
D
CK
Q
7474
DTACK
R/W
AS
MC68000
LINEAR CIRCUITRY OMITTED FOR CLARITY.
FOR THE AD7828 ONLY
**
*
Figure 17. AD7824/AD7828–MC68000 Interface
TMS32010 MICROCOMPUTER
A TMS32010 interface is shown in Figure 18. The AD7824/
AD7828 is operating in Mode 1 (i.e., no µP WAIT states). The
ADC is mapped at a port address. The following I/O instruction
starts a conversion and reads the previous conversion result into
the accumulator.
IN, A PA (PA = PORT ADDRESS)
The port address (000 to 111) selects the analog channel to be
converted. When conversion is complete, a second I/O instruc-
tion (IN, A PA) reads the up-to-date data into the accumulator
and starts another conversion. A delay of 2.5 µs must be allowed
between conversions.
DATA BUS
A2**
AD7824*
AD7828*
A1
A0
CS
RD
DB7
DB0
PA 2
PA 1
PA 0
MEN
DEN
D7
D0
TMS32010
LINEAR CIRCUITRY OMITTED FOR CLARITY.
FOR THE AD7828 ONLY
**
*
Figure 18. AD7824/AD7828–TMS32010 Interface
