MC68HC05L28B MOTOROLA [Motorola, Inc], MC68HC05L28B Datasheet - Page 102

• Manufacturer Part Number: MC68HC05L28B
• Description: Flexible general-purpose microcomputer
• Manufacturer: MOTOROLA [Motorola, Inc]

9
9.3
The external analog voltage value to be processed by the A/D converter is sampled on an internal
capacitor through a resistive path, provided by input-selection switches and a sampling aperture
time switch, as shown in Figure 9-2. Sampling time is limited to 12 bus clock cycles. After sampling,
the analog value is stored on the capacitor and held until the end of conversion. During this hold
time, the analog input is disconnected from the internal A/D system and the external voltage
source sees a high impedance input.
The equivalent analog input during sampling is an RC low-pass filter with a minimum resistance
of 50 k
temperature).
MOTOROLA
9-6
ADx analog input
and a capacitance of at least 10pF (these are typical values measured at room
Note:
Analog
input
pin
The analog switch is closed during the 12 cycle sample time only.
Figure 9-2 Electrical model of an A/D input pin
Input protection device
< 2pF
A/D CONVERTER
+ ~20V
- ~0.7V
junction
leakage
400 nA
50k
capacitance
DAC
10pF
V
RL
MC68HC05L28
TPG