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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
The ZX-40 series devices (other than the ZX-40n) require a serial EEPROM in which to store your
program’s code.  (The ZX-40n uses 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.
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
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