When AO is low, the byte addressed contains the 8MSBs.
When AO is high, the byte addressed contains the 4LSBs
from the conversion followed by four logic zeros which
have been forced by the control logic. The left-justified
formats of the two 8-bit bytes are shown in Figure 8. The
design of the ADC574A guarantees that the AO input may be
toggled at any time with no damage to the converter; the
outputs which are tied together as illustrated in Figure 9
cannot be enabled at the same time.
In the majority of applications the read operation will be
attempted only after the conversion is complete and the
STATUS output has gone low. In those situations requiring
the earliest possible access to the data, the read may be
started as much as 1.15µs (tDD max + tHS min) before
STATUS goes low. Refer to Figure 7 for these timing
relationships.
Word 1
Word 2
Processor
Converter
DB7 DB6
DB5
DB9
DB4
DB8
DB3
DB7
DB2
DB6
DB1
DB5
DB0
DB4
DB7 DB6
DB3 DB2
DB5
DB1
DB4
DB0
DB3
0
DB2
0
DB1
0
DB0
0
DB11 DB10
FIGURE 8. 12-Bit Data Format for 8-Bit Systems.
STATUS 28
2
4
12/8
AO
DB11 (MSB) 27
26
25
24
23
22
AO
Address
Bus
Data
Bus
ADC574A
21
20
19
18
17
DB0 (LSB) 16
Digital Common 15
FIGURE 9. Connection to an 8-Bit Bus.
®
10
ADC574A
BB [ BURR-BROWN CORPORATION ]
