ModuleWare Reference Guide - Hornad

Three-state bus (tribus)This part uses two tri-state buffers cascaded together toimplement a three-state bidirectional bus.The input port din drives the first tri-state buffer and the resultis placed in the inout port tin. This port drives the secondbuffer and the result is placed in the output port dout.The first buffer is enabled, when the scalar port dena has avalue 1.The second buffer is enabled when the scalar port tena has a value 1.This part is equivalent to 2n 1-bit tristate inverters where n is the port width.FunctionFor every bit:Logic PartsThree-state bus (tribus)douttin= tin= Z= din= Z(enabled, tena = 1)(disabled; tena not equal to 1)(enabled, dena = 1)(disabled, dena not equal to 1)Truth TablesTable 2-33. Three-state Bus Truth Tabledin(i) dena tin(i) as input tin(i)0 1 0 00 1 1 X1 1 0 X1 1 1 10 0 0 00 0 1 11 0 0 01 0 1 1Table 2-34. Three-state Bus Truth Tabletin(i) tena dout(i)0 1 01 1 1ModuleWare Reference Manual, Library Version 1.9 53September 18, 2008