This firmware is intended to run on Atmel ATmega163 (499 bytes for program memory) or AT90S8515 (298 Bytes for program memory). Communications with the terminal is via RS-232 at 9600 baud. Use 8 data bits, 1 stop bit, and no parity. The RXD pin and TXD pin should be connected to an inverting RS-232 interface. The Maxim MAX-232 and the discreet interface shown in the schematic which is described in Atmel Application note AVR-910, are examples of such interfaces. If the RXD pin is grounded when the chip comes out of reset, either from application of power or after an external reset, the contents of the EEPROM will be loaded and executed by the interpreter.
AttoBasic - schematic

If the contents of the EEPROM is loaded when the EEPROM is in an erased state some of the internal pointers will be set inappropriately, so it is advisable to type "NEW" and "SAVE" to initialize the EEPROM. A weak internal pull-up is applied to the RXD pin. Weak internal pullups are also applied to PD3 and PD4 for the DS Interface. Applications with particularly low parasitic capacitance on the DS Interface lines can omit the external pullup resistors on these two pins. MEMORY, I/O: PEEK, POKE, plus dedicated I/O instructions for 8 and 10 bit pulse width modulation, 8 bit A-to-D, byte I/O and single bit manipulation and testing on Ports A thorgh D, and rudimentary DS Interface instructions DSCOMMAND, DSDATA, and DSREAD. Programs are stored in internal RAM. Some RAM is available for use as an array via PEEK and POKE commands. 26 Variables (A..Z) are supported. All arithmetic and variables are byte-wide. Strings are not directly supported. Keep statements to one simple exression per line. Line editor supports destructive backspace (delete key), line replacement , line deletion, and line insertion. Valid line numbers range is 0..255. Lines entered with a numeral in the first column will be stored, others will be interpreted immediately. SAVE and LOAD commands save and load the program from the on-chip EEPROM. If RXD pin is held low during power-up, EEPROM code will be automatically loaded and executed. The interpreter is...

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