old	Alternate Products
PIC16F84-1998	pic16f15243
PIC16F877a-2001	PIC16F18877

specific controller

MPASM	XC8 Assembler
LIST P = DeviceName	PROCESSOR DeviceName

LIST (indicates specific controller, e.g., LIST P=18F452) unique to PIC assembler.

Include Files

MPASM	XC8 Assembler
INCLUDE <DeviceName.INC>	#include <xc.inc>

Set device’s configuration bits

MPASM	XC8 Assembler
__CONFIG	The CONFIG directive with appropriate settings and values

MPASM:

__CONFIG  _WDT_OFF & _PWRTE_ON & _CP_OFF

PIC Assembler:

CONFIG WDT   = OFF
CONFIG PWRTE = ON
CONFIG CP    = OFF

Label name

Labels in PIC Assembler must be followed by a colon “:”
In MPASM the colon is optional.

Constants and Radices

By default, MPASM interprets the numeric constants as hexadecimal values.
PIC Assembler interprets them by default as decimal values!
This is where explicit definition can help with code portability.

MPASM	XC8 Assembler
-	RADIX DEC

numeric constants

Table 3-1. Equivalent Constants Radix Specifiers

MPASM

movlw b'10110011' ; binary value
movlw o'72' ;octal value
movlw d'34' ;decimal value
movlw 4F ;hexadecimal value
movlw ‘b’ ;ASCII value

PIC Assembler

movlw 10110011B ;binary value
movlw 72q ;octal value
movlw 34 ;decimal value
movlw 04Fh ;hexadecimal value
movlw ‘b’ ;ASCII value

lacing Psects into Memory

MPASM	XC8 Assembler
ORG	PSECT

MPASM supports absolute mode, using the ORG directive, or relocatable mode, using program sections.
PIC Assembler only supports the relocatable mode.

Since the tutorials use the absolute mode you will need to remove the ORG directive and add a program section for the code and data.
I have just added a code section for all the instructions and used the already defined equates to access the data memory variables (user registers).
So, I have just replaced the ORG directive with the PSECT directive like this:

PSECT MyCode,class=CODE,delta=2

To make sure the linker places this section at address 000h, we need to provide an additional command line parameter:
Go to “Project Properties” > “pic-as Global Options” > “Additional Options:” and add the following parameter (without spaces!):

-Wl,-pMyCode=0h

About section name

Where “MyCode” is the section name, “class=CODE” tells the linker to use the default code section, “delta=2" tells the linker the number of data bytes that are associated with each address.

We can also just define a code section like this:

PSECT code

But I’d rather define my own code section “MyCode” so that I can tell the linker to specifically place this code section at the zero address.
Otherwise, the linker will place it somewhere else, and it will probably overwrite the RC oscillator calibration instruction at the top of the memory (address 0FFh).

class - psect flag

Table 5-2. Assembler-provided Psects and Linker Classes

Psect name	Linker class	Target device families	Purpose
code	CODE	All	To hold executable code
eedata	EEDATA	All	To hold data in EEPROM
data	STRCODE	Baseline, Mid-range	To hold data in program memory
udata	RAM	All	To hold objects allocatable anywhere in GPR
udata_bankn	BANKN	All	To hold object allocatable in a particular data memory bank
udata_shr	COMMON	Baseline, Mid-range	To hold objects allocatable in common memory

delta - psect flag

The delta psect flag defines the size of the addressable unit.
In other words, the number of data bytes that are associated with each address.
With PIC Mid-range and Baseline devices, the program memory space is word addressable; so, psects in this space must use a delta of 2.
That is to say, each address in program memory requires 2 bytes of data in the HEX file to define their contents.
So, addresses in the HEX file will not match addresses in the program memory.
The data memory space on these devices is byte addressable; so, psects in this space must use a delta of 1.
This is the default delta value.
All memory spaces on PIC18 devices are byte addressable; so a delta of 1 (the default) should be used for all psects on these devices.
The redefinition of a psect with conflicting delta values can lead to phase errors being issued by the assembler.

global - psect flag

the global psect flag indicates that the linker should concatenate this psect with global psects in other modules and which have the same name.

Directive

Table 4-1.Equivalent Directives

MPASM Directive	PIC Assembler Replacement
ACCESS_OVR	A psect with the ovrld flag set
__BADRAM and __BADROM No replacement
BANSISEL	The instruction sequence to write indirect access registers
BANKSEL	The BANKSEL directive (no change required)
CBLOCK	Consider the SET/EQU directives, or DS.
CODE	The code psect or similar
CODE_PACK	The code psect or similar
__CONFIG	The CONFIG directive with appropriate settings and values
CONFIG	The CONFIG directive with appropriate settings and values
CONSTANT	The EQU directive
DA	Consider the DB or IRPC directives
DATA	Consider the DW directive
DB	The DB directive
DE	Consider the DB directive inside a suitable psect
#DEFINE	The #define preprocessor directive
DT	The IRP directive
DTM	The IRP directive
DW	The DW or DB directive
ELSE	The ELSE directive (no change required)
END	The END directive (no change required)
ENDC	No replacement
ENDM	The ENDM directive (no change required)
ENDW	No replacement
EQU	The EQU directive (no change required)
ERROR	The ERROR directive
ERRORLEVEL	Consider the -w driver option
EXITM	No replacement
EXPAND	The EXPAND directive (no change required)
EXTERN	The EXTRN directive (note different spelling)
FILL	Consider the –fill driver option
GLOBAL	The GLOBAL directive (no change required)
IDATA	A psect with the initial values in program memory and another reserving space for the data objects
IDATA_ACS	A psect with the initial values in program memory and another reserving space for the data objects
IF	The IF directive (no change required)
IFDEF	Consider the #ifdef preprocessor directive
IFNDEF	Consider the #ifndef preprocessor directive
#INCLUDE	The #include preprocessor directive
LIST	The LIST directive or consider alternate assembler options
LOCAL	The LOCAL directive (no change required)
MACRO	The MACRO directive (no change required)
__MAXRAM _and __MAXROM	No replacement
MESSG	The MESSG directive (no change required)
NOEXPAND	The NOEXPAND directive (no change required)
NOLIST	The NOLIST directive (no change required)
ORG	Consider the ORG directive
PAGE	No replacement
PAGESEL	The PAGESEL directive (no change required)
PAGESELW	Consider the PAGESEL directive
PROCESSOR	The PROCESSOR directive (no change required)
RADIX	The RADIX directive (no change required)
RES	Consider the DS directive
SET	The SET directive (no change required)
SPACE	The SPACE directive (no change required)
SUBTITLE	The SUBTITLE directive (no change required)
TITLE	The TITLE directive (no change required)
UDATA	The udata_bankn psect or similar
UDATA_ACS	The udata_acs psect or similar
UDATA_OVR	A psect with the ovrld flag set
UDATA_SHR	A psect with the ovrld flag set
#UNDEFINE	The #undefine preprocessor directive
VARIABLE	Consider the SET directive
WHILE	Consider the REPT directive

List Directive

TABLE 4-2: LIST DIRECTIVE OPTIONS

|Option| Default| Description| |-|-| |b=nnn| 8 |Set tab spaces.| |c=nnn| 132| Set column width.| |f=format| INHX8
M
|Set the hex file output. format can be INHX32, INHX8M, or INHX8S.
Note: Hex file format is set in the IDE (Build Options dialog.)
| |free| FIXED| Use free-format parser. Provided for backward compatibility.| |fixed| FIXED| Use fixed-format parser.| |mm={ON|OFF}| On| Print memory map in list file.| |n=nnn| 60| Set lines per page.| |p=type| None| Set processor type; for example, PIC16F877. See also processor.
Note: Processor type is set in MPLAB IDE or MPLAB X IDE projects.
|pe=type| None| Set processor type and enable extended instruction set, for example; LIST pe=PIC18F4620
Only valid with processors which support the extended instruction set and the generic processor PIC18XXX. Is overridden by command-line option /y- or -y- (disable extended instruction set).
Note: Processor type is set in MPLAB IDE or MPLAB X IDE projects.
|r=radix| hex| Set radix: hex, dec, oct. See also radix.| |st={ON|OFF}| On| Print symbol table in list file.| |t={ON|OFF}| Off| Truncate lines of listing (otherwise wrap).| |w={0|1|2}| 0| Set the message level. See also errorlevel.| |x={ON|OFF}| On| Turn macro expansion on or off|

Define a Block Of Constants

Do not use cblock or equ to define variable location names for relocatable code.

CBLOCK = accumulative equ

CBLOCK

cblock 0x20 ; name_1 will be assigned 20
name_1, name_2 ; name_2, 21 and so on
name_3, name_4 ; name_4 is assigned 23.
endc

    name_1    EQU 0x20
    name_2    EQU 0x21
    name_3    EQU 0x22
    name_4    EQU 0x23

TRIS register

In order to define a pin as input or output pin, the right combination of zeros and ones must be written in TRIS register.

TRIS: The Register Input/output State.

TRISA: which is the address of the Tri-State register for PortA
...
TRISC: which is the address of the Tri-State register for PortC

banksel

The file registers of the pic are held in banks, some are shared across all banks and some program data can also be shared across all banks but this is obviously wasteful of memory so it’s limited to select registers and shared data.

Special function registers, SFR’s are used to control, configure and check the pic’s status.
These tend to be on different banks to the programs variables so you need to change banks or your program will be accessing the wrong bank.
This is where the ‘banksel’ instruction comes in. It makes sure you are addressing the correct memory bank.

When to use banksel

first access of any UDATA section variable
first access of register after a subroutine call/external module
when accessing a banked special function register
after having accessed a banked SFR(special function register)

When to don’t need to use banksel

after first access to a UDATA variable other UDATA variables are in the same bank
UDATA_SHR variables are available on any bank
accessing Non-banked SFR’s like STATUS etc.. can be done from any bank

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MPASM to MPLAB XC8 PIC Assembler