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This chapter introduces the std_logic_1164 logic system used for all gate-level and system-level simulation components in Hades. Where the traditional Boolean logic only supports the binary values (0/1), the std_logic system includes a total of nine logic values. The extra values are used to model undefined, illegal, or weakly driven signals and cover most situations encountered in digital logic design.

Most circuits only use the values 0 and 1 during a simulation, while U indicates signals that have not yet been initialized, and X indicates real malfunctions. The remaining values, namely Z, W, L, and H, are necessary to model signals (buses) with multiple drivers. The special D value is not used at all during simulation, but provided to support logic synthesis tools.

 spacer  Logic values and glow-mode colors applet  webstart  print 
 spacer  Basic std_logic_1164 functions applet  webstart  print 
 spacer  Interactive switches  applet  webstart  print 
 spacer  Basic gates applet  webstart  print 
 spacer  Hexadecimal (4 bit) switch and display applet  webstart  print 
 spacer  Clock generator component applet  webstart  print 
 spacer  Two-phase clock generator applet  webstart  print 
 spacer  Buses and the std_logic_1164 resolution function applet  webstart  print 
 spacer  Wired-AND bus demonstration applet  webstart  print 
 spacer  Detectors and counters demonstration applet  webstart  print 
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