Assembly Language Subroutines Lance A. Leventhal Winthrop Saville OSBORNE/McGraw-Hill Berkeley, California Disclaimer of Warranties and. Assembly Language Subroutines. The authors and the publisher apparently assume that if you don’t know which computers use the microprocessor. assembly language subroutines / Lance A. Leventhal, Winthrop Saville. Subjects: Assembly languages (Electronic computers) · (Microprocessor) > .

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Jump indirect to address at the top of the stack. The uses the following common conventions: Neither of the next two sequences should be used to test for stack over- flow or underflow, since intervening instructions for example, a single JSR or RTS could change the stack pointer by more than 1.

6502 assembly language subroutines

The book is as thorough as just about every Osborne publication, and just about as complex. They are not as com- mon as the handshaking functions governed by the peripheral control register.

However, you can produce ordinary indirect addressing by using the postindexed indirect indexed addressing mode with index register Y set to 0. Volume I — Basic Langauge, 2nd ed. It is thus critical to determine how often instructions are being executed and to work on loops in the order of their frequency of execution. We could leave the accumulator intact by saving it in the stack originally and restoring it afterward. The program multiplies the row size number of columns in a row times the row subscript since the elements are stored by rows and adds the product to the column subscript.

Sybroutines accumulator, setting the Carry flag if the result is zero. This sequence allows you to transfer control past parameters, data, or other nonexecutable items. Then you will not have to save the parameters or assign space in the stack for the results they will replace some or all of the original parameters. In particular, one can handle arrays of two-byte elements by using ASL A to double an index in the accumulator.


Be careful, however, of the fact that the processor adds 1 to the address before proceeding. Note that the size of the rightmost subscript is simply the size of the elements in bytes ; the size of the next subscript is the size of subroutknes elements times the maximum value of the rightmost languabe plus 1, etc. Logically OR the accumulator with the contents of an indexed address obtained using index register X and the base 17E0 Complement a assemhly location.

Shift the accumulator right 1 bit arithmetically, preserving the sign most “significant bit. The main program sssembly then know that the service routine has been executed. Withoutabox Submit to Film Festivals.

In the case of a decrement, yOu must check for first. Index register X is also used in preindexing indexed indirect addressing. As with direct addressing, a special zero page mode is provided.

The does not automatically save any registers except the program counter and the status register. The program then shifts the more significant digit left four bits and combines it with the Registers Used: The assembler will not produce an error message, since is a valid decimal dumber. There are no bit registers and no operations that act on bit quantities.

Lookup tables generally use extra memory but save execution time. lanbuage

Branch if Lower Unsigned. Note that with JMP, the indirect address may be located anywhere asembly memory; it is not restricted to page 0. A simple way to avoid problems in programs that use Addition or Subtraction instructions is to save the original D flag in the stack, assign D the appropriate value, and restore the original value before exiting.

Catalog Record: 6502 assembly language subroutines | Hathi Trust Digital Library

A logic means that a switch is closed or a display is lit. The assem- bler will not produce an error message, since 40 is a valid decimal number. One can also simplify array processing by reducing the multiplications required in indexing to additions. Thus, in the case of signed numbers, we must allow for the following two possibilities: Axsembly organize the readings as a two-dimensional array TO, Jlanguafe I is the tank number 1, 2, or 3 and J is the number of the position in the tank 1, 2, 3, or 4.


The second version is slower but reentrant. Remember that an input device normally starts out in the not ready state — it has no data available although the computer is ready to accept data. The processor must respond under pro- gram control. Introduction to the Program Section The program section contains sets of assembly language subroutines for the microprocessor. The instruction LSR ASL shifts the accumulator or a memory location right left one position, filling the leftmost rightmost bit with a 0.

Chapter 6 contains additional examples of arithmetic programs.

Full text of ” assembly language subroutines”

Convert one 8-bit code to another using a lookup table. ComiXology Thousands of Digital Comics. AmazonGlobal Ship Orders Internationally.

The data direction registers are easy to initialize. The ele- ment occupies the starting address and the address one larger; elements may be organized with either the less significant byte or the more significant byte in the starting address.

Amazon Renewed Refurbished products with a warranty. Note the convenience here of having the status register at the top, rather than underneath the return address. The copy must be updated every time the actual assfmbly is changed. Decimal subtract accumulator from the contents of memory location ADDR and place difference in accumulator. Each subroutine is documented with an introductory sec- tion and comments; each is followed by at jeast one example of its use.

Thus, the programmer should consider laguage following guidelines when writing interrupt-driven code for the Always refers to an address on page 1. A sequence that will asembly a jump, if the result of the increment is 00 thus implying the production of a carryis illustrated below.