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Text File  |  1992-01-18  |  5.2 KB  |  137 lines
  1. DOCUMENTATION LAYOUT    V 2.0
  2. =============================
  3.  
  4.  
  5.  
  6. I added two multiplexer to switch between 7 and 14 MHz. This was necessary
  7. because some software had problems at 14 MHz (e.g. Janus.library). The
  8. multiplexers I use has four channels with each two inputs and one output.
  9. Five signals (\VMA, \VPA, E-CLK, \DTACK and CLK) must be switched.
  10. So we need two multiplexers.
  11.  
  12. The multiplexer MUST! be a fast (F) type, otherwise the gate delay is
  13. be too long.
  14.  
  15. Here's how I connected it :
  16.  
  17.     16       15       14       13       12       11       10        9
  18.      |        |        |        |        |        |        |        |
  19. |-------------------------------------------------------------------------|
  20. |   +5V      EN     \DTACK   \DTACK   \DTACK     CLK      CLK      CLK    |
  21. |                   original  sync      out     7MHz     14MHz     out    |
  22. |                                                                         |
  23. |                                74 F 157                                 |
  24. |                                                                         |
  25. |           \VPA     \VPA     \VPA     E-CLK    E-CLK    E-CLK            |
  26. |   SEL    original  sync      out    original  DIV 2     out     Ground  |
  27. |-------------------------------------------------------------------------|
  28.      |        |        |        |        |        |        |        |
  29.      1        2        3        4        5        6        7        8
  30.  
  31.  
  32.  
  33.     16       15       14       13       12       11       10        9
  34.      |        |        |        |        |        |        |        |
  35. |-------------------------------------------------------------------------|
  36. |   +5V      EN                                 \VMA     \VMA      \VMA   |
  37. |                                              orginal   sync       out   |
  38. |                                                                         |
  39. |                                74 F 157                                 |
  40. |                                                                         |
  41. |                                                                         |
  42. |   SEL                                                           Ground  |
  43. |-------------------------------------------------------------------------|
  44.      |        |        |        |        |        |        |        |
  45.      1        2        3        4        5        6        7        8
  46.  
  47.  
  48.  
  49. The SEL is now synconized with 7 MHz so that you simply can switch between
  50. 7 and 14 MHz without \HALT (this was in the last release) while the Amiga
  51. is running and it shouldn't crash.
  52. This is done with a D-flipflop 74F74 (also fast (F) type!) :
  53.  
  54.    14       13       12       11       10        9        8
  55.     |        |        |        |        |        |        |
  56. |------------------------------------------------------------|
  57. |  +5V                                                       |
  58. |                                                            |
  59. |                          74 F 74                           |
  60. |                                                            |
  61. |                                                            |
  62. |           Switch                                           |
  63. |  +5V      input    7 MHz     +5V      SEL            Ground|
  64. |------------------------------------------------------------|
  65.      |        |        |        |        |        |       |
  66.      1        2        3        4        5        6       7
  67.  
  68.  
  69. (Switch input is +5V or Ground)
  70. (SEL is select output used by the 74F157 as input)
  71.  
  72.  
  73.  
  74. The next thing I added is a jumper (J1). This will vary the way \DTACK is
  75. syncronized. The middle must be connected with the left OR the right side.
  76. (74LS27/2 is connected with 74LS74/9 or with \DTACK - some machines only
  77. work one way ... because it's an Amiga !)
  78.  
  79. To smooth the flanks I added eight (C3-C10) capacitors (100nF).
  80.  
  81.  
  82.  
  83. REBUILDING :
  84. -----------------------------------------------------------------------------
  85.  
  86. It's double sided. The lower side is the reflected image.
  87. I made a hardcopy and it looks well. For better results use a 2:1 scale if
  88. you can.
  89. There's only one through-connect (between the 74F157 and 74LS112).
  90.  
  91. Amiga 500 owner should not plug the MC 68000 in a socket (it's to high), but
  92. they will need a 64 pin socket as a distance to the ROM.
  93.  
  94. The accelerator plugs by two 32 pin strips in the CPU-socket.
  95.  
  96.  
  97. Parts you need besides :
  98.  
  99. - 2x 74 F 157
  100. - 1x 74 F 74
  101. - 1x 74 F 86 (replace for 74 LS 86)
  102. - 8x 100nF
  103. - 2x 22pF
  104. - 2x 560 Ohm
  105. - 1x 10KOhm
  106. - 1x 64 pin socket
  107. - 2x 32 pin strips
  108. - 1x single switch
  109.  
  110. -----------------------------------------------------------------------------
  111.  
  112. Wanting to know the acceleration precise I wrote a CPU performance test
  113. program (See performance directory). Look at my tests and things come clear.
  114.  
  115.  
  116. Special thanks to Livio Plos for his great and cheap Amiga accelerator.
  117. Thanks Livio !
  118.  
  119. Any critiques, suggestions, questions, etc. are welcome !
  120.  
  121. Joerg Richter
  122. Dresdener Strasse 21
  123. 2150 Buxtehude
  124. GERMANY
  125.  
  126. EMail: Joerg.Richter@arbi.informatik.uni-oldenburg.de
  127.  
  128.  
  129. ---------------------------------------------------------------------------
  130.  
  131. How to get a PCB :
  132.  
  133. If you want this PCB you may buy it from Joerg or Livio for DM 50,- or US 30$,
  134. this include shareware contribute.
  135.  
  136.  
  137.