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File List  |  1987-09-25  |  2.8 KB  |  78 lines
  1. PAL16R4
  2. PAL FOR 6821 TO PC BUS INTERFACE  J.R. DRUMMOND 24/1/87
  3. CONTROLS BUS ACCESS
  4.  
  5. CLK /BS   /IOR   /IOW  RESET  PIN6  PIN7  PIN8  PIN9  GND
  6. /OC RESB  SELB   E     C      PIN16 CS    RWB   READY VCC
  7.  
  8.  
  9. IF (VCC)    /SELB  =  BS * IOR  +  BS * IOW
  10.  
  11. IF (VCC)    /RESB  = RESET
  12.  
  13. IF (/SELB)  /READY =  /CS  +  CS * /C  +  CS * C * E * IOW
  14.  
  15. IF (VCC)    /RWB   = IOW
  16.  
  17.             /CS   :=  /CS * /C  +  /CS * E
  18.                      +  C * /E * /BS  +  /CS * C * /E * /IOR * /IOW
  19.                      +  CS * C * /E * /IOW
  20.  
  21.             /C    :=  /C * /E  +  /CS * C * /E
  22.                      +  CS * C * /E * /BS  +  CS * C * /E * /IOW
  23.  
  24.             /E    :=  C * /E  +  /CS * C * E
  25.                       +  CS * C * E * /BS  +  CS * C * E * /IOR
  26.  
  27.  
  28. DESCRIPTION
  29.  
  30.                      ------u------
  31.           CLK      1-|           |-20     VCC
  32.                      |           |
  33.           /BS      2-|           |-19     READY
  34.                      |           |
  35.           /IOR     3-|           |-18     RWB
  36.                      |           |
  37.           /IOW     4-|          R|-17     CS
  38.                      |           |
  39.           RESET    5-|          R|-16     PIN16
  40.                      |   16R4    |
  41.           PIN6     6-|          R|-15     C
  42.                      |           |
  43.           PIN7     7-|          R|-14     E
  44.                      |           |
  45.           PIN8     8-|           |-13     SELB
  46.                      |           |
  47.           PIN9     9-|           |-12     RESB
  48.                      |           |
  49.           GND     10-|___________|-11     /OC
  50.  
  51.  
  52.            CS  C  E
  53. -->
  54.            0   1  1
  55.            0   1  0
  56.             +---------------------------+-------------------------+
  57.             |                           |                         |
  58.        /BS + /IOR./IOW                BS.IOW                   BS.IOR
  59.  
  60.                                       1   0   0               1  0  0
  61.                                       1   0   1               1  0  1
  62.                                       1   1   1                      <-+
  63.                                                               1  1  1  |BS.IOR
  64.                                                                 -------+
  65.                                                 <---------------
  66.                                                 <-+
  67.                                       1   1   0   |BS.IOW
  68.                                           --------+
  69.                      <--------------------
  70.            0   0   0
  71.            0   0   1
  72.   <------------
  73.  
  74.  
  75.        NO ACCESS                  WRITE CYCLE               READ CYCLE
  76.  
  77. READY ASSERTED AT LOOP POINT IN BOTH CYCLES AND BEYOND