PIC16C54B-20I/SS Microchip Technology, PIC16C54B-20I/SS Datasheet - Page 30

• Manufacturer Part Number: PIC16C54B-20I/SS
• Description: MICRO CTRL 512 20MHZ OTP 20SSOP
• Manufacturer: Microchip Technology
• Series: PIC® 16Cr

Specifications of PIC16C54B-20I/SS

• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 20MHz
• Peripherals: POR, WDT
• Number Of I /o: 12
• Program Memory Size: 768B (512 x 12)
• Program Memory Type: OTP
• Ram Size: 25 x 8
• Voltage - Supply (vcc/vdd): 3 V ~ 5.5 V
• Oscillator Type: External
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 20-SSOP
• Lead Free Status / RoHS Status: Request inventory verification / Request inventory verification
• Eeprom Size: -
• Data Converters: -
• Connectivity: -

PIC16C5X
6.2
An 8-bit counter is available as a prescaler for the
Timer0 module, or as a postscaler for the Watchdog
Timer (WDT) (WDT postscaler not implemented on
PIC16C52), respectively (Section 6.1.2). For simplicity,
this counter is being referred to as “prescaler”
throughout this data sheet. Note that the prescaler
may be used by either the Timer0 module or the WDT,
but not both. Thus, a prescaler assignment for the
Timer0 module means that there is no prescaler for
the WDT, and vice-versa.
The PSA and PS2:PS0 bits (OPTION<3:0>) determine
prescaler assignment and prescale ratio.
When assigned to the Timer0 module, all instructions
writing to the TMR0 register (e.g., CLRF 1, MOVWF 1,
BSF 1,x, etc.) will clear the prescaler. When assigned
to WDT, a CLRWDT instruction will clear the prescaler
along with the WDT. The prescaler is neither readable
nor writable. On a RESET, the prescaler contains all
'0's.
6.2.1
The prescaler assignment is fully under software control
(i.e., it can be changed “on the fly” during program
execution). To avoid an unintended device RESET, the
FIGURE 6-6:
DS30453B-page 30
Prescaler
SWITCHING PRESCALER ASSIGNMENT
WDT Enable bit
Note: T0CS, T0SE, PSA, PS2:PS0 are bits in the OPTION register.
T0CKI
Watchdog
pin
Timer
T
CY
WDT not implemented on PIC16C52.
BLOCK DIAGRAM OF THE TIMER0/WDT PRESCALER
( = Fosc/4)
T0SE
0
1
PSA
M
U
X
0
1
T0CS
M
U
X
Preliminary
0
8-bit Prescaler
8 - to - 1MUX
Time-Out
8
MUX
WDT
1
0
1
following instruction sequence (Example 6-1) must be
executed when changing the prescaler assignment from
Timer0 to the WDT.
EXAMPLE 6-1:
To change prescaler from the WDT to the Timer0
module, use the sequence shown in Example 6-2. This
sequence must be used even if the WDT is disabled. A
CLRWDT instruction should be executed before switching
the prescaler.
EXAMPLE 6-2:
CLRWDT
MOVLW
OPTION
PSA
1.CLRWDT
2.CLRF
3.MOVLW
4.OPTION
5.CLRWDT
6.MOVLW
7.OPTION
M
U
X
PSA
'xxxx0xxx'
TMR0
'00xx1111’b ;These 3 lines (5, 6, 7)
'00xx1xxx’b ;Set Postscaler to
PS2:PS0
Cycles
Sync
2
CHANGING PRESCALER
(TIMER0 WDT)
CHANGING PRESCALER
(WDT TIMER0)
1998 Microchip Technology Inc.
;Clear WDT
;Clear TMR0 & Prescaler
; are required only if
; desired
;PS<2:0> are 000 or 001
; desired WDT rate
;Clear WDT and
;prescaler
;Select TMR0, new
;prescale value and
;clock source
TMR0 reg
Data Bus
8