adc0858civ National Semiconductor Corporation, adc0858civ Datasheet - Page 18

• Manufacturer Part Number: adc0858civ
• Description: 8-bit Analog Data Acquisition And Monitoring Systems
• Manufacturer: National Semiconductor Corporation

2 0 Memory Access Modes
The ADC0851 8 has an internal RAM with sixteen memory
locations (one location for the upper limit and one for the
lower limit for each of the 8 input channels) Each memory
location is 8 bits wide An 8-bit limit word representing an
upper or lower limit boundary can either be written to or read
from the RAM The ADC0851 uses only four memory loca-
tions for the four boundary limits corresponding to the two
inputs The eight channel ADC0858 however makes use of
all sixteen memory locations
Each memory location is accessed by a specific address as
shown by Table II(a) and (b) Note that even addresses cor-
respond to the lower limits while the odd addresses corre-
spond to the upper limits The ADC0851 and ADC0858 both
use 4 bits (A3
ADC0851 decodes only the two LSBs of the address data
while ignoring the two MSBs
L0
L0
A3
A3
X
X
X
X
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
L1
L1
RAM Address
RAM Address
A2
A2
X
X
X
X
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
L2
L2
TABLE IIa RAM Address and
TABLE IIb RAM Address and
Limit Data for ADC0851
Limit Data for ADC0858
Limit Data (ADC0851)
Limit Data (ADC0858)
L3
L3
A1
A1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
A0) to address the RAM however
L4
L4
A0
A0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
L5
L5
CH0 – Lower Limit
CH0 – Upper Limit
CH1 – Lower Limit
CH1 – Upper Limit
CH0 – Lower Limit
CH0 – Upper Limit
CH1 – Lower Limit
CH1 – Upper Limit
CH2 – Lower Limit
CH2 – Upper Limit
CH3 – Lower Limit
CH3 – Upper Limit
CH4 – Lower Limit
CH4 – Upper Limit
CH5 – Lower Limit
CH5 – Upper Limit
CH6 – Lower Limit
CH6 – Upper Limit
CH7 – Lower Limit
CH7 – Upper Limit
Channel and Limit
Channel and Limit
L6
L6
Corresponding
Corresponding
L7
L7
18
2 1 WRITE ONE LIMIT
This mode is used to update a single memory location in the
limit RAM An 8-bit limit word is written to the location point-
ed to by the limit address From Table I we can see that to
initiate the operation of the device in the ‘‘write one limit’’
mode the mode address has to be 1 0 0 1 The data format
for the input word is as shown below
Data Input (DI) Word ADC0851 or ADC0858
TL H 11021 – 31