PIC16F1937-I/ML Microchip Technology, PIC16F1937-I/ML Datasheet - Page 6

• 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

OVERFLOW/UNDERFLOW
The new stack has 16 entries but a 5-bit Stack Pointer.
This Stack Pointer is visible as the STKPTR register in
Bank 31. When the MSb of STKPTR is set after a call
or interrupt, the stack is considered in overflow. If the
optional Reset is enabled, the Program Counter will go
immediately to ‘0’ and the reset condition flag in PCON
will indicate a Stack Reset. If the STKPTR reads 31 (all
bits set) then the stack is considered empty. A return
(RETURN, RETLW, RETFIE) when the stack is empty is
an underflow. If the optional Reset is enabled, the Pro-
gram Counter will go immediately to 0x0000 and the
Reset condition flag in PCON will indicate a Stack
Reset. If the optional Reset is not enabled, the stack
will continue to operate but underflow and overflows
will simply wrap around the 16 entry stack. The Stack
Overflow and Underflow bits can be checked to deter-
mine if a stack is out of bounds.
DEBUGGING ACCESS
The legacy PIC12/16 shared the 8 levels of stack
with the in-circuit debugging firmware. This could be
very restrictive. The enhanced PIC12/16 has an
additional stack reserved for the debugging firm-
ware. This eliminates the possibility of running out of
stack when using Debug mode. When debugging,
the Stack Reset option becomes a break point to
help determine the cause of the stack problem. The
stack access mechanism is also used by the debug-
ger to provide the engineer visibility to the call chain
that led the software to its present state.
USER ACCESS
The user has full access to the 16 levels of user stack.
The debug stack is unavailable. Access to the stack is
through three registers; Stack Pointer (STKPTR), Top-
of-Stack High (TOSH) and Top-of-Stack Low (TOSL).
These registers are located in Bank 31.
MODIFYING THE STACK
Modifying the stack requires that the STKPTR be
adjusted to point to the entry that needs updating, and
TOSH/TOSL be changed to reflect the modification.
The STKPTR register always points at the last entry
placed on the stack. When a call or interrupt is
executed, the STKPTR register is incremented and the
PC is stored at the new TOSH/TOSL location. Make
sure that interrupts are disabled before modifying the
stack.
Relative Branching
Relative branching is branching to a target address that
is based upon the current address. With the legacy
PIC12/16, we often wrote code such as the following:
DS41375A-page 6
When we write the $-1 we are requesting a relative
branch, except the assembler is converting that into an
absolute branch. The payload size of CALL and GOTO
created the 2k page size so CALL and GOTO contribute
to the paging problem.
The enhanced PIC12/16 adds a BRA and BRW relative
branch. The BRA allows you to branch +256 or -255
instructions from the current program counter. The pre-
vious code example would look like this.
Because Label is an absolute address, the assembler
will convert the absolute address to a relative address
by subtracting the current Program Counter from the
destination address. If the $-1 syntax is used, it will
work in the same way. If the constant -1 is supplied to
BRA it will not work because -1 specifies an address at
the end of the program memory and that will most likely
be out of range.
FASTER TABLE READS
The BRW instruction is also a relative branch but the
reach is from 0 to 255. The relative address for BRW is
contained in the W register. This allows the traditional
table read method to execute much faster without
regard for table location.
EXAMPLE 1:
In the example above, the letter ‘t’ is returned to the
calling function.
Table
Label
Label
GOTO
DECFSZ
DECFSZ
BRA
MOVLW
BRW
RETLW
RETLW
RETLW
RETLW
RETLW
RETLW
RETLW
RETLW
$-1
delay
delay
Label
© 2009 Microchip Technology Inc.
3
‘a’
‘ ‘
‘s’
‘t’
‘r’
‘i’
‘n’
‘g’