参数资料
型号: MC68HC05SB7
厂商: FREESCALE SEMICONDUCTOR INC
元件分类: 微控制器/微处理器
英文描述: 8-BIT, MROM, 2.1 MHz, MICROCONTROLLER, PDSO28
封装: MO-150, SSOP-28
文件页数: 33/170页
文件大小: 2161K
代理商: MC68HC05SB7
GENERAL RELEASE SPECIFICATION
August 27, 1998
MOTOROLA
ANALOG SUBSYSTEM
MC68HC05SB7
15-30
REV 2.1
15.7
CURRENT SOURCE FEATURES
The internal current source connected to the CAP pin supplies about 100
A of
current when the ramp discharge device is disabled and the current source is
active. Therefore this current source can be used in an application if the ISEN
enable bit is set to power up the current source is enabled by setting the A/D con-
version method to manual Mode 0 (ATD1 and ATD2 cleared) and the charge cur-
rent enabled (CHG set).
15.8
SAMPLE AND HOLD
When using the internal sample capacitor to capture a voltage for later conver-
sion, the HOLD and DHOLD bit must be cleared rst before changing any channel
selection. If both the HOLD (or DHOLD) bit and the channel selection are
changed on the same write cycle, the sample may be corrupted during the switch-
ing transitions.
NOTE
The sample capacitor can be affected by excessive noise created with respect to
the device’s VSS pin such that it may appear to leak down or charge up depending
on the voltage level stored on the sample capacitor. It is recommended to avoid
switching large currents through the port pins while a voltage is to remain stored
on the same capacitor.
The additional option of adding an offset voltage to the bottom of the sample
capacitor allows unknown voltages near VSS to be sampled and then shifted up
past the comparator offset and the device offset caused by a single VSS return pin.
The offset also provides a means to measure the internal VSS level regardless of
the comparator offset in order to determine NOFF as described in Section 15.5.
15.9
PORT B INTERACTION WITH ANALOG INPUTS
The analog subsystem is connected directly to the Port B I/O pins without any
intervening gates. It is therefore possible to measure the voltages on Port B pins
set as inputs; or to have the analog voltage measurements corrupted by Port B
pins set as outputs.
Table 15-8. Voltage Comparator Setup Conditions
Current
Source
Enable
Discharge
Device
Disable
Port B Pin
as Inputs
Prog. Timer
Input Capture
Source
ISEN = 0
DDRB4 = 0
DDRB5 = 0
ICEN = 0
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