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ZBasic Language Reference 166 ZX Microcontroller Family #XC-957ND) in a cylindrical package. The capacitor value to use depends somewhat on the layout (e.g. stray capacitance). Values in the range of 22pF to 27pF have been used successfully in various situations. ZX-40 Series Clock Source If you already have a clock source at the required frequency you can feed that signal directly to pin 13. In this case there would be no connection to pin 12. Program Memory Some ZX-40 series devices require a serial EEPROM in which to store your program’s code. (The ZX- 40n, ZX-40r and ZX-40s use internal Flash memory for Program Memory.) The recommended device to use is the Atmel AT25256A (Digi-Key #AT25256A-10PI-2.7-ND). Note, particularly, that the older part without the A suffix will not work due to its slower speed. An EEPROM capable of operation at 7.5MHz or more is required. An alternate part is the ON Semiconductor CAT25256LI-G (Digi-Key #ON Semiconductor CAT25256LI-G-ND). The recommended connection to the ZX-40 series is shown below. The value of the pullup resistor is non-critical. Anything from 4.7K to 22K should work well. Higher values will reduce power consumption somewhat. ZX-40 Series Program Memory (VM models only) With firmware versions v1.1 and later, the Atmel 25HP512 (Digi-Key #AT25HP512-10PI2.7-ND) can also be used for applications that require larger EEPROM space. The electrical connections for this device are identical to those shown above. However, since this device has different characteristics than the AT25256A, special configuration is required. See Section 9.2 for more information.