PIC16F1937-I/ML Microchip Technology, PIC16F1937-I/ML Datasheet - Page 13

• Manufacturer Part Number: PIC16F1937-I/ML
• Description: IC PIC MCU FLASH 512KX14 44-QFN
• Manufacturer: Microchip Technology
• Series: PIC® XLP™ 16Fr

Specifications of PIC16F1937-I/ML

• Core Size: 8-Bit
• Program Memory Size: 14KB (8K x 14)
• Core Processor: PIC
• Speed: 32MHz
• Connectivity: I²C, LIN, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, LCD, POR, PWM, WDT
• Number Of I /o: 36
• Program Memory Type: FLASH
• Eeprom Size: 256 x 8
• Ram Size: 512 x 8
• Voltage - Supply (vcc/vdd): 1.8 V ~ 5.5 V
• Data Converters: A/D 14x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 44-QFN
• Controller Family/series: PIC16F
• No. Of I/o's: 36
• Eeprom Memory Size: 256Byte
• Ram Memory Size: 512Byte
• Cpu Speed: 32MHz
• No. Of Timers: 5
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ARITHMETIC
Arithmetic on the PIC12/16 is a very basic function but
can be full of small frustrations when working with
multi-byte data. For example, the legacy ADD
instructions do not include an add with Carry, so multi-
byte operations require additional instructions to
precondition the next Most Significant Byte (MSB)
based upon the results of the previous add. New
instructions added to the enhanced PIC12/16 simplify
this work, shaving many instructions from common
algorithms.
Multi-byte Add
Adding two 16-bit values with a PIC12/16 is usually
done as follows:
This code works quite well but has 2 extra cycles in the
middle, due to the missing add with Carry. This code
can be converted to the enhanced PIC12/16 as follows:
The enhanced version saves two instructions. If 16-bit
values are used extensively, the savings will add up.
Multi-byte Subtract
Subtract is similar to add because the Borrow flag must
be handled in the following computations. The legacy
code is as follows:
© 2009 Microchip Technology Inc.
Add16_enhanced
Add16
Sub16
ADDWF
MOVF
ADDWF
MOVF
BTFSC
ADDLW
SUBWF msb_b,f
MOVF
ADDWF
MOVF
ADDWFC
MOVF
SUBWF lsb_b,f
MOVF
BTFSS STATUS,C
ADDLW 0xFF
lsb_a,w
msb_a,w
msb_b,f
msb_b,f
lsb_a,w
lsb_b,f
msb_a,w
lsb_a,w
lsb_b,f
msb_a,w
STATUS,C
0x01
The enhanced version is as follows:
The enhanced version of subtract saves two
instructions.
Shifting
Shifting is the fastest method to divide or multiply by a
power of two, therefore, it is often used instead of
rotates. A rotate instruction can be made to operate like
a shift simply be preconditioning the Carry flag. The
legacy code is as follows:
This code will work but the W register is overwritten by
the first rotate. The ASRF instruction simplifies this
problem by handling the sign extension in hardware.
This is faster by requiring less code. Arithmetic
_Left_Shift does not need to perform a sign exten-
sion. It simply brings zero into the LSB.
If sign extend is not required, the code is simpler.
Simply clearing the Carry flag before performing the
rotate will create a logical shift. These examples can be
converted to single enhanced PIC12/16 instructions.
Logical_Right_Shift
Logical_Left_Shift
Sub16_enhanced
Arithmetic_Right_Shift
RRF
ASRF val,f
RLF
BCF
RRF
BCF
MOVF
SUBWF lsb_b,f
MOVF
SUBWFB msb_b,f
RLF
val,w ;save the MSB
val,f ;rotate right
val,f
STATUS,C
val,f
STATUS,C
lsb_a,w
msb_a,w
in the Carry
(corrupt W
with sign extend.
DS41375A-page 13