184 Chapter 9 the actual error. Consequently, the message generated is not always entirely accurate. For example, the incorrect instruction mnemonic at line 58 caused the assembler to misinterpret `Count' as an illegal op-code. The PROCESSOR directive was misplaced, causing a non-fatal warning, which would not itself prevent successful assembly of the program. The TRIS instruction also caused a warning in the MPLAB assembler, because its use is not recommended, but will still be successfully assembled. It is used in our examples because the alternative method of port initialization, using register bank selection, is more complicated. The instruction mnemonic DECF was misspelt as DEC, causing the errors at line 58. This contributed to the register label count being misinterpreted. The register label `Timer' was missed out of the EQU statements at the top of the program, causing the error at line 71. The jump destination `again1' has been incorrectly labeled `again', causing the error at line 73. Finally, the END directive had been omitted at the end of the program, causing the message `Expected (END)'. The message `Using default destination of 1 (file)' refers to the fact that the full syntax for MOVWF instruction has not been used. Using the full syntax, the destination for the result of the operation is specified as the file register or the working register, by placing a W (0) or F (1) after the destination register number or label. In the examples throughout this text, we take advantage of the assumption by the assembler that the destination is the file register if not specified in the instruction; this simplifies the source code. When the error messages have been studied carefully, and printed out if necessary, the source code must be re-edited and reassembled until it is correct. The different levels of error message (message, warning and error) can be selectively suppressed in the list file output using the list file options with the directive LIST. These options can also be set in the Project, Build Options dialogue in MPLAB by selecting the Output Category under the Assembler tab, then the preferred Diagnostics level. 9.2. Logical Errors When all syntax errors have been eliminated the program will assemble successfully, and the hex file will be created. However, this does not necessarily mean that it will function correctly when downloaded to the chip; in fact, it probably won't! Usually there will be logical errors, particularly when learning the programming method. Mistakes in the program functional sequence or syntax will prevent it operating as required. For instance, the wrong register may be operated on or a loop may execute correctly, but the wrong number of times. There may also be `run-time' errors, that is, mistakes in the program logic that only show up when the program is actually executed. A typical run-time error is `Stack Overflow', which is caused by CALLing