参数资料
型号: PIC16C621-20/SS
元件分类: 微控制器/微处理器
英文描述: 8-BIT, OTPROM, 20 MHz, RISC MICROCONTROLLER, PDSO20
封装: 0.209 INCH, PLASTIC, MO-150, SSOP-20
文件页数: 61/121页
文件大小: 1202K
代理商: PIC16C621-20/SS
PIC16C62X
DS30235H-page 44
1999 Microchip Technology Inc.
EXAMPLE 8-1:
VOLTAGE REFERENCE
CONFIGURATION
8.2
Voltage Reference Accuracy/Error
The full range of VSS to VDD cannot be realized due to
the construction of the module. The transistors on the
top and bottom of the resistor ladder network
(Figure 8-1) keep VREF from approaching VSS or VDD.
The voltage reference is VDD derived and therefore, the
VREF output changes with fluctuations in VDD. The
tested absolute accuracy of the voltage reference can
be found in Table 12-2.
8.3
Operation During Sleep
When the device wakes up from sleep through an
interrupt or a Watchdog Timer time-out, the contents of
the VRCON register are not affected. To minimize
current consumption in SLEEP mode, the voltage
reference should be disabled.
MOVLW
0x02
; 4 Inputs Muxed
MOVWF
CMCON
; to 2 comps.
BSF
STATUS,RP0
; go to Bank 1
MOVLW
0x0F
; RA3-RA0 are
MOVWF
TRISA
; inputs
MOVLW
0xA6
; enable VREF
MOVWF
VRCON
; low range
; set VR<3:0>=6
BCF
STATUS,RP0
; go to Bank 0
CALL
DELAY10
; 10
s delay
8.4
Effects of a Reset
A device reset disables the voltage reference by clear-
ing bit VREN (VRCON<7>). This reset also disconnects
the reference from the RA2 pin by clearing bit VROE
(VRCON<6>) and selects the high voltage range by
clearing bit VRR (VRCON<5>). The VREF value select
bits, VRCON<3:0>, are also cleared.
8.5
Connection Considerations
The voltage reference module operates independently
of the comparator module. The output of the reference
generator may be connected to the RA2 pin if the
TRISA<2> bit is set and the VROE bit, VRCON<6>, is
set. Enabling the voltage reference output onto the RA2
pin with an input signal present will increase current
consumption. Connecting RA2 as a digital output with
VREF enabled will also increase current consumption.
The RA2 pin can be used as a simple D/A output with
limited drive capability. Due to the limited drive
capability, a buffer must be used in conjunction with the
voltage reference output for external connections to
VREF.
shows
an
example
buffering
technique.
FIGURE 8-2:
VOLTAGE REFERENCE OUTPUT BUFFER EXAMPLE
TABLE 8-1:
REGISTERS ASSOCIATED WITH VOLTAGE REFERENCE
Note:
- = Unimplemented, read as "0"
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Value On
POR
Value On
All Other
Resets
9Fh
VRCON
VREN
VROE
VRR
VR3
VR2
VR1
VR0
000- 0000
1Fh
CMCON
C2OUT
C1OUT
CIS
CM2
CM1
CM0
00-- 0000
85h
TRISA
TRISA4
TRISA3
TRISA2
TRISA1
TRISA0
---1 1111
VREF Output
+
VREF
Module
Voltage
Reference
Output
Impedance
R(1)
RA2
Note 1: R is dependent upon the Voltage Reference Configuration VRCON<3:0> and VRCON<5>.
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