PIC Assembler Modules

For Non-Commercial Use Only

I would appreciate to be credited within your project, if you use any of the source code below. If you have an interesting project going on, I'll be glad about feedback.

The software below comes with no guarantee or warranty except for my good intentions. Further the use of this code implies that the user has a fundamental understanding of electronics and its risks. I'm not responsible for any harm or damage, caused by inproper use of any of the code below.
Any commercial use of parts or all of this code requires the permission of the author.

Table of Contents [Toc]

General
Standard Modules
Dot Matrix LCD Modules
   LCD Display Driver Routines
   LCD Display Conversion Routines
Serial Communication Modules (RS232)
Notes on Modules
General Recommendations
   Known Limitations of MPLAB IDE
   Technical Hints

General  [Toc] [Top]

Modules are source code blocks, which can be included in the MAIN PROGRAM by simply adding the command line:
  #include "C:/ (...) m_bank.asm"
The code will be inline expanded. All you need is to specify the necessary registers in front of the include statement in the main program, e.g.

Standard Modules   [Toc] [Top]

Assembler include files: General macros to ease assembler handling, e.g. macros BANK0, BANK1

For demo-programs or complete applications, refer to 'Projects'   [click here]
 

Dot Matrix LCD Modules   [Toc] [Top]

Assembler include files: Display drivers for dot matrix LCD displays.   (Hitachi HD44780 compatibles)
 

Dot Matrix LCD Display 4 lines x 20 characters

Dot Matrix LCD Display 2 lines x 40 characters

LCD Display Driver Routines   [Toc] [Top]

Download the PDF schematic to illustrate the connectivity of both 'classes' of LCD driver routines:

• Modules m_lcd.asm, m_lcdx.asm, m_lcd_bf.asm, m_lcdxbf.asm: working only on entire ports ([1..7], without [0]),
  e.g. PortB[1..7] on PIC16F84,
  or PortB[1..7], PortC[1..7], PortD[1..7] on PIC16F77
• Modules m_lcde.asm, m_lcde_bf.asm, m_lcdexbf.asm: working on separate, customizable ports,
  e.g. PortB[0..2] for control lines & PortA[0..3] for data lines on PIC16F84, PIC16F7x,
  or PortC[5..7] for control lines & PortD[0..3] for data lines on PIC16F77, or ...
  Note that the data lines have to be on the low nibble of the port.

For demo-programs or complete applications, refer to 'Projects'   [click here]
 

LCD Display Conversion Routines   [Toc] [Top]

For demo-programs or complete applications, refer to 'Projects'   [click here]
 

Serial Communication Modules (RS232)   [Toc] [Top]

Software-based RS232 communication for all Microchip PIC MCUs. The routines handle all aspects of RS232 transmission and reception, based on busy waits. The MCU port for RS232 transmission can be selected freely by the user, provided it is an active digital push/pull port. The MCU port for RS232 reception is limited to PORTB,0 due to its own interrupt flag.

Note that for external interrupts, such as the RB0/INT pin or PORTB change interrupt, the latency will be three to four instruction cycles. The exact latency depends on when the interrupt occurs. The latency is the same for both one and two cycle instructions.
(=> see Microchip PIC16/17 Microcontroller Databook.)

For those, who are not familiar with interfacing a PIC to the RS232 using a MAX232 :   RS232-Interface.pdf   (9.7 kB)

For demo-programs or complete applications, refer to 'Projects'   [click here]
 

Notes on Modules   [Toc] [Top]

• Code is optimized for 1. small memory, and 2. optimal execution time.
• If extern sources are called from within modules, set absolute pathes. Please refer to Known Limitations of MPLAB IDE below.
• Declare and define the required registers and statements in the MAIN.
• Declarations of constants and registers need to be listed in the MAIN before the '#include' statement of the modules, since most modules are referencing specific constants and registers (therefore they need to be defined at that time).
   

General Recommendations   [Toc] [Top]

• Manage the used registers in a clear structured way.
• For prototyping, it is recommended to introduce temporarily dedicated registers for each new code segment. At the end, when everything runs properly, you can start to optimize the design in order to share as much registers as possible to save memory space. Otherwise, you run the risk of getting data consistency problems - bugs, which are really hard to solve!
• Provide dedicated registers for interrupt handling! Do not call subroutines from the interrupt service routine (ISR), which are executed during normal operation. If so, ensure to perform a complete context save of all registers being used within this subroutine.
• Interrupt flags have to be cleared by software before re-enabling the 'global interrupt enable bit' (GIE) and exiting the ISR. Otherwise, recursive ISR calling occurs.
• At the beginning of the ISR, disable the 'global interrupt enable bit' (GIE). In case different interrupt sources have to be served, it may be necessary to disable also the related 'interrupt source enable bit' (e.g. INTF of RB0/INT pin). See next recommendation
• On ISR exit, make sure to reset the interrupt flag of the source, which triggered the interrupt. But perform re-enabling of the corresponding 'interrupt source enable bit' at the end of the corresponding service routine:
  - If the interrupt service is entirely completed within the ISR, re-enabling is suitable at the end of the ISR. This applies only, if disabling of the interrupt source has been carried out at the beginning of the ISR.
  - If parts of the interrupt service are carried out during normal operation, re-enabling the interrupt source is most suitable at the end of the external code part. In this case, disabling the specific interrupt source at the beginning of the ISR is stringent, otherwise we face lost of data or a system crash due to return address stack overflow. This method owns a further advantage: A subsequent interrupt already having been triggered before re-activation and originating from the same source is not omitted and will immediately be served. (This is because the interrupt flag bit gets still set, when the interrupt is temporarily disabled. When unmasking this interrupt source, the interrupt is immediately triggered.)
   

Known Limitations of MPLAB IDE   [Toc] [Top]

• Previously MPLAB worked with the old MS DOS 8.3 naming convention (so set paths with old notation).
  However, recent MPLAB versions seem to accept also longer file names. That's why my include files sometimes have strange names.
• Note that there is also an upper limitation on the amount of characters for file names including path.
  Without using the MPLINK linker, i.e. for absolute/non-relocationable assembler code, file names including path are somehow restricted to 62 characters (see MPLAB IDE Quick Reference, p.3).
• '#include' - commands in the MAIN could be relative (..\..\xyz.asm) or absolute paths (C:\abc\xyz.asm).
• '#include' - commands in extern source have to be absolute paths (if extern source is called with relative path).
   

Technical Hints   [Toc] [Top]

• If you use 'set' instead of 'equ', you can assign different labels to the same register. This is very useful, if you need temporary registers in different modules. But be careful that you do not write and access the same register alternating in 2 different procedures. This results in nice bugs or possibly endless loops.
• 'equ' is exclusive, i.e. it accepts only one label for each register.
• If you want to create a 16 bit assembler look-up table very quickly, have a look at the
  Automatic Table Generator for MPLAB Assembler.
• To specify exact periods (e.g. with busy wait module m_wait.asm), I use quite often the MPLAB stopwatch. This is a very convenient cycle-accurate timer, which takes both 1 cycle (e.g. incf) and 2 cycle instructions (e.g. goto) as well as special instruction mnemonics (e.g. bnc, subcf) into account.
  I just let the simulator run to the wait statement or loop to be measured, reset the stopwatch, and let it again simulate until after the wait statement:

Last updated: 2010/05/14