mc68hc916y3 Freescale Semiconductor, Inc, mc68hc916y3 Datasheet - Page 213

• Manufacturer Part Number: mc68hc916y3
• Description: Mc68hc16y3 16 Bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

10.6.1 Multiplexer
10.6.2 Sample Capacitor and Buffer Amplifier
MC68HC16Y3/916Y3
USER’S MANUAL
The multiplexer selects one of 16 sources for conversion. Eight sources are internal
and eight are external. Multiplexer operation is controlled by channel selection field
CD:CA in register ADCTL1. Table 10-2 shows the different multiplexer channel sourc-
es. The multiplexer contains positive and negative stress protection circuitry. This cir-
cuitry prevents voltages on other input channels from affecting the current conversion.
Each of the eight external input channels is associated with a sample capacitor and
share a single sample buffer amplifier. After a conversion is initiated, the multiplexer
output is connected to the sample capacitor at the input of the sample buffer amplifier
for the first two ADC clock cycles of the sampling period. The sample amplifier buffers
the input channel from the relatively large capacitance of the RC DAC array.
During the second two clock cycles of a sampling period, the sample capacitor is dis-
connected from the multiplexer, and the sample buffer amplifier charges the RC DAC
array with the value stored in the sample capacitor.
During the third portion of a sampling period, both sample capacitor and buffer ampli-
fier are bypassed, and multiplexer input charges the DAC array directly. The length of
this third portion of a sampling period is determined by the value of the STS field in
ADCTL0.
Table 10-2 Multiplexer Channel Sources
Freescale Semiconductor, Inc.
For More Information On This Product,
[CD:CA] Value
ANALOG-TO-DIGITAL CONVERTER
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
Go to: www.freescale.com
(V
Test/Reserved
Input Source
RH
Reserved
Reserved
Reserved
Reserved
AN0
AN1
AN2
AN3
AN4
AN5
AN6
AN7
V
– V
V
RH
RL
RL
) / 2
MOTOROLA
10-5