The Americas. Latin America. Arab World. Middle Ages. Local History. Book History. History of Science. Gender Studies. Tropical Medicine. Natural History. Legal Studies. Start vector for disk or non-cartridge software. Initialization address for the disk boot. If the following bits are set to one , then these interrupts arc enabled bit decimal values are in parentheses :. Monitored by both keyboard, display, cassette and screen handlers.
Internal realtime clock. When location 19 reaches , it and 20 are reset to zero and location 18 is incremented by one every Indirect buffer address register page zero. Temporary pointer to the current disk buffer. Command for CIO vector. Stores the CIO command; used to find the offset in the command table for the correct vector to the handler routine. Disk file manager pointer.
The disk utilities pointer. Printer timeout, called every printer status request. Initialized to 30, which represents 32 seconds the value is 64 seconds per 60 increments in this register ; typical timeout for the Atari printer is five seconds. The value is set by your printer handler software.
It is updated after each printer status request operation. Print buffer pointer; points to the current position byte in the print buffer. Ranges from zero to the value in location Print buffer size of printer record for current mode. Normal buffer size and line size equals 40 bytes; double-width print equals 20 bytes most printers use their own control codes for expanded print ; sideways printing equals 29 bytes Atari printer only.
Printer status request equals four. The printer handler checks to see if the same value is in PBPNT and, if so, sends the contents of the buffer to the printer.
Temporary register used by the printer handler for the value of the character being output to the printer. Handler index number. Set by the OS as an index to the device name table for the currently open file. Device number or drive number. Initialized to one.
Put byte routine address set by the OS. Auxiliary information first byte used in OPEN to specify the type of file access needed. CIO working variables, also used by some serial port functions. Auxiliary information second byte.
The byte being accessed within the sector noted in locations 44 and Each IOCB block is 16 bytes long. Other sources indicate that the X register also contains this information. Spare byte. Internal status storage. To adequately identify these RAM locations, our format gives the decimal value of the location, the equivalent hexadecimal base 16 value, the number of contiguous locations serving the specified function, the name used in the Operating System listing published by Atari, and a description of the function.
For example:. This notation is arbitary but is the consensus method of indicating base 16 numbers. The low memory locations that follow are used by the Operating System for housekeeping functions. Figure 1 shows the gross memory map. This should give you some idea of where BASIC resides in memory, what part of memory is used and unused, etc.
Not all of the 65, possible memory locations are described, nor need to be. Most of memory is left "free" for the user. These values govern execution of user programs and are important for programmers to know. When set equal to 0 then powerup retry. When equal to 1 then successful disk boot. When equal to 2 then successful cassette boot. JSR indirect thru here to initialize application. Screen handler opens S: only if no RAM needed below this address. Monitored by keyboard, also screen editor. This is set to 0 when break key is pressed.
Mapping The Atari - Revised Edition By Ian Chadwick The comprehensive sourcebook and memory guide. For beginning and veteran programmers of the Atari. MAPPING. THE ATARI. Ian Chadwick. Introduction by Bill Wilkinson. A comprehensive sourcebook and memory guide for beginning and veteran programmers.
Called frame counter, initialized to 0 and overflows to 0. Used as a temporary Page Zero pointer to current disk buffer. Used to find correct vector to the handler routine. Used as vector to FMS.
Points to a buffer for utilities package. Typical timeout for the is 5 seconds. Initialized to 30 sec. Set to if no file opened. Initialized to 1. CIO working variables. Z Spare bytes local CIO use. Default is Default is one. Zero indicates checksum follows transmission. Retain and count number of beeps requested of beep routine by cassette handler during open processing; one beep for play, two for record.
POKE 0 and it won't buzz. Start key checked, if pressed then CKEY is set. Incremented every 4 seconds by stage 1 Vblank. Margins are user alterable. Ignored in every mode but 0. Range 0 Range 0 - hibyte. Home position is 0,0 for both graphics and text.
Used to restore character after cursor moves. A logical line can contain up to 3 physical lines.