AD7570 Просмотр технического описания (PDF) - Analog Devices
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AD7570 Datasheet PDF : 12 Pages
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8
MICROPROCESSOR INTERFACE
Since most 8-bitmicroprocessors
utilize a bidirectio~al data
bus, each input peripheral (such as the AD7570) must be
capable of isolating itself from the data bus when other I/O
devices, memory, or the CPU takes control of the bus. The
AD7570 output data and status (BUSY) lines all utilize three-
state logic to provide this requirement.
Figure 16 illustrates a method of interfacing a TTY keyboard
and printer to the AD7570, using an 8080 microprocessor as
the interface controller.
3. LBEN is enabled, and the eight least significant data bits
(DBO-DB7) are applied to the data bus for subsequent trans-
fer to the 8080. When the data transfer is complete, LBEN
is disabled, and DBO-DB7 return to their floating state.
4. HBEN is enabled, and the two most significant AD7570 data
bits (DB8 and DB9) are applied to the data bus for subse-
quent transfer to the 8080. When the data transfer is
complete, HBEN is disabled, and DB8 and DB9 return to
their floating state.
The program (stored in Read Only Memory) waits for a key-
stroke on the TTY keyboard. When a keystroke is detected,
5. The 8080 (in conjunction with the programmed Read Only
Memory) performs a binary to decimal conversion.
an AID conversion is started. When conversion is complete,
~
~
the 8080 reads in the binary data from the AD7570, converts
it to ASCII, and prints out the decimal number (preceded by a
carriage return and line feed) on the teletype printer.
More specifically, the main sequence of events would be as
follows:
8 1. When a TTY keystroke is detected by the CPU (via the
OUAR/T Receiver), a "convert start" (STRT) is applied to
the AD7570.
B2. BSEN is enabled, placing BUSY (conversion status) on the
S data bus. When the 8080 detects BUSY = 1, conversion is
O complete, and BSEN is disabled, causing BUSY to return to
its floating state.
6. SWE (Status Word Enable) on the UAR/T transmitter is
enabled, applying XBMT (Transmitter Buffer Empty) to
the data bus. When a Logic "1" is detected by the 8080,
SWEis disabled, and XBMT returns to a floating state.
7. TDS (Transmitter Data Strobe) strobes the converted
decimal number into the UAR/T transmitter for subsequent
serial clocking into the keyboard.
The interface scheme shown below is only one example of a
myriad of possible data acquisition/control systems which
could conveniently use the AD7570 to provide digital data to
a microprocessor or minicomputer bus.
8 LETE A15
A8
DBFLlN . MEMR . A2
A7
ADDRESS BUSS
I
DBFLlN . MEMR . A4
AO
DBFLlN
8 ~
8080
DO-D7
BSEN
HBEN
AD7570 ADC
(MSBI
(lSB)
-, , BOSY DB9 8 7 6 5 4 3 2 1 BDO
DBFLlN . MEMR
DATA BUSS
DO
DO
DO
D7
D1 DO D7 D6
Dol 07'
03 D2 D1 DO
8 .
WR
DBFLlN
SYNC
FROM
KEYBOARD
RDA
RSI
UAR/T REC
RDAR RDE SWE
XBMT
UAR/T XMT
TDS
. WR AO
DBFLlN
WR A2
TO PRINTER
. . MEMR AO
DBFLlN . MEMR . AT
D
ClK
:J1 . SYNC
MEMR
Q
O.MEMR
Figure 16. Microprocessor Controlled TTY IADC Interface
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