MC68HC705JP7 Datasheet, PDF (114/242 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Analog Subsystem
with respect to the external V_SS pin. Turning on the V_SS MUX to the
channel select bus connects it to this internal AV_SS reference line.
When making A/D conversions, this AV_SS offset gets placed on the
external ramping capacitor since the discharge device on the PB0/AN0
pin discharges the external capacitor to the internal AV_SS line. Under
these circumstances, the positive input (+) to comparator 2 will always
be higher than the negative input (–) until the negative input reaches the
AV_SS offset voltage plus any offset in comparator 2.
Therefore, input voltages cannot be resolved if they are less than the
sum of the AV_SS offset and the comparator offset, because they will
always yield a low output from the comparator.
Table 8-2. Channel Select Bus Combinations
Analog Multiplex Register
Channel Select Bus Connected to:
VREF
MUX4
MUX3
MUX2
MUX1
V_DD
PB4/AN4/
TCMP
PB3/AN3/
TCAP
PB2/AN2
PB1/AN1
V_SS
0
0
0
0
0 Hi-Z
Hi-Z
Hi-Z
Hi-Z
Hi-Z
On
X⁽¹⁾
0
0
0
1 Hi-Z
Hi-Z
Hi-Z
Hi-Z
On
Hi-Z
X⁽¹⁾
0
0
1
0 Hi-Z
Hi-Z
Hi-Z
On
Hi-Z Hi-Z
X⁽¹⁾
0
0
1
1 Hi-Z
Hi-Z
Hi-Z
On
On
Hi-Z
X⁽¹⁾
0
1
0
0 Hi-Z
Hi-Z
On
Hi-Z
Hi-Z Hi-Z
X⁽¹⁾
0
1
0
1 Hi-Z
Hi-Z
On
Hi-Z
On
Hi-Z
X⁽¹⁾
0
1
1
0 Hi-Z
Hi-Z
On
On
Hi-Z Hi-Z
X⁽¹⁾
0
1
1
1 Hi-Z
Hi-Z
On
On
On
Hi-Z
X⁽¹⁾
1
0
0
0 Hi-Z
On
Hi-Z
Hi-Z
Hi-Z Hi-Z
X⁽¹⁾
1
0
0
1 Hi-Z
On
Hi-Z
Hi-Z
On
Hi-Z
X⁽¹⁾
1
0
1
0 Hi-Z
On
Hi-Z
On
Hi-Z Hi-Z
X⁽¹⁾
1
0
1
1 Hi-Z
On
Hi-Z
On
On
Hi-Z
X⁽¹⁾
1
1
0
0 Hi-Z
On
On
Hi-Z
Hi-Z Hi-Z
X⁽¹⁾
1
1
0
1 Hi-Z
On
On
Hi-Z
On
Hi-Z
X⁽¹⁾
1
1
1
0 Hi-Z
On
On
On
Hi-Z Hi-Z
X⁽¹⁾
1
1
1
1 Hi Z
On
On
On
On
Hi Z
1. Don/t care
Advance Information
114
MC68HC705JJ7 • MC68HC705JP7 — REV 4
Analog Subsystem
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