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PAL6821.LST
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1987-09-25
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3KB
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78 lines
PAL16R4
PAL FOR 6821 TO PC BUS INTERFACE J.R. DRUMMOND 24/1/87
CONTROLS BUS ACCESS
CLK /BS /IOR /IOW RESET PIN6 PIN7 PIN8 PIN9 GND
/OC RESB SELB E C PIN16 CS RWB READY VCC
IF (VCC) /SELB = BS * IOR + BS * IOW
IF (VCC) /RESB = RESET
IF (/SELB) /READY = /CS + CS * /C + CS * C * E * IOW
IF (VCC) /RWB = IOW
/CS := /CS * /C + /CS * E
+ C * /E * /BS + /CS * C * /E * /IOR * /IOW
+ CS * C * /E * /IOW
/C := /C * /E + /CS * C * /E
+ CS * C * /E * /BS + CS * C * /E * /IOW
/E := C * /E + /CS * C * E
+ CS * C * E * /BS + CS * C * E * /IOR
DESCRIPTION
------u------
CLK 1-| |-20 VCC
| |
/BS 2-| |-19 READY
| |
/IOR 3-| |-18 RWB
| |
/IOW 4-| R|-17 CS
| |
RESET 5-| R|-16 PIN16
| 16R4 |
PIN6 6-| R|-15 C
| |
PIN7 7-| R|-14 E
| |
PIN8 8-| |-13 SELB
| |
PIN9 9-| |-12 RESB
| |
GND 10-|___________|-11 /OC
CS C E
-->
0 1 1
0 1 0
+---------------------------+-------------------------+
| | |
/BS + /IOR./IOW BS.IOW BS.IOR
1 0 0 1 0 0
1 0 1 1 0 1
1 1 1 <-+
1 1 1 |BS.IOR
-------+
<---------------
<-+
1 1 0 |BS.IOW
--------+
<--------------------
0 0 0
0 0 1
<------------
NO ACCESS WRITE CYCLE READ CYCLE
READY ASSERTED AT LOOP POINT IN BOTH CYCLES AND BEYOND