Xi8088 Version 2.0

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Introduction

Xi 8088 IBM PC/XT compatible processor board

Features

  • ISA board form factor
  • Support of PS/2 keyboard and mouse
  • Built-in real time clock with NVRAM

Board Layout

Click on any chip for more information

74ALS175 Quad D flip-flopPS/2 ConnectorPS/2 ConnectorReset SwitchBiLevelLEDPN222ACrystal14.31818MhzTrimmerCapacitor5-53pFDIPSwitch8PinDIPSwitch12PinPCSpeakerCellHolderCR2032Crystal24Mhz29F010825974F24474F57374F245I8087I808874ALS175828474ALS7474ALS0474ALS0274ALS7474ALS17574HCT11N74ALS00AS6C4008825974F24574ALS2074ALS0074ALS13974LS92AS6C400874F57374F573828874ALS0274LS13874ALS13974ALS0074LS0674ALS0474LS67074F24574F24574ALS3274ALS7474ALS32VT82C428237DS12885825474F244Xi 8088 - Complete Board.png
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Proposed Improvements

Sometimes the non-turbo crystal fails to oscillate. The proposed improvement to this circuit is seen below. I will test it further and introduce this change in the next revision of the board. Roughly speaking the formula to determine the values of the load capacitors C1 and C2 is (Load Capacitance of the Crystal – Capacitance of the IC and PCB) x 2

For a crystal with load capacitance of 20pf (find in datasheet) and board and chip with built-in 5pf capacitance then the capacitors you should use will be around 30pf. But since capacitors have different tolerances and measuring such small capacitances is hard with shitty equipment then experimenting with different value capacitors is your best bet.

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