Update README.md

README.md

@@ -90,3 +90,20 @@ revision 1.2 was made because there were some errors in the lettering below the
 
 I have also designed a very simple variant of the TZXDuino, an Arduino nano based playback device that can convert a .TZX file for a sinclair spectrum, or ZX-81 from a SD-Card to an audio signal that can be used to load a cassette file (game) into a sinclair computer, you can find it as the TZXDuino Pico project on the mahjongg2 github pages. I plan to use it to test the cassete interface of my ZX81+38 clone. The PCB is very small only 37.1 mm wide, and 47.2 mm high and it is a 2 layer board.
 
+#getting an EPROM in 2022 
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+from various sources I heard that EPROM's (OTP's) are almost unobtainable. I have done a small research, and yes, it seems OTP ROM's are very hard to get. I found however one option that will work, you can buy an 28C64 for about ten euro. from Reichelt its an 8K x 8 reprogrammable (EEPROM), you can buy it from here: https://www.reichelt.nl/nl/nl/eeprom-64-kb-8-k-x-8-5-v-150-ns-pdip-28-28c64-150-p1946.html?&trstct=pol_2&nbc=1
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+yes, you need to change a wire bridge, as the 28C64 has a different pinout than a 27C64 but that isn't a very big deal.
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+Here is a diagram showing the differences between a 27C256 and an 28C256
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+[img]https://revspace.nl/images/thumb/6/68/Rom_pinouts_for_ZX81%2B38_resized.png/707px-Rom_pinouts_for_ZX81%2B38_resized.png[/img]
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+For a 28C64 the only real difference is that pin 27 must be tied high so that /WR is inactive, so switch jp10 to tie pin 27 high, not low.
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+It is expected that 27C256's will become available beginning next year (2023).
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+Another solution is to buy a new old stock EPROM , the ones with a glass windows form a Chinese reseller these have the exact same pinout as modern OTP's as OTP's simply contain the same DIE (chip) as UV erasable EPROM's, so they have the exact same pinouts as OTP's.
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