Digital Circuit Boards: Mach 1 GHz

2.22 The Network Program

The following program outline can accommodate a large group of interconnected transmission lines (network). The basic program provides for one logic transition at t = 0. The program can be modified to allow for multiple logic transitions occurring at different times. The increment of time should be small enough that waves are detected, as they reach the ends of each segment.

The program below stops after 300 waves have been assigned. This number is arbitrary and can be changed to fit the problem being solved.

PROGRAM OUTLINE

Draw the network. Assign a number to each transmission line segment.

100 Provide initial voltages, termination and characteristic impedances, transit times.

120 Provide reflection and transmission coefficients for every wave transition, reflection, and termination. Let n be the program counter. Set n = 1. Let m be the wave counter. Set m = 1.

130 Set WV(1) to a voltage, a location LOC(1), a time of arrival TM(1) in picoseconds and a direction DIR(1). This is the initial wave that occurs after a logic switch closes.

140 Increment t (time) in picoseconds.

150 Increment n. IF n > 300 then END. Note that n cycles through all m wave numbers.

160 If DIR(n) = 0 then set n = 0: (End of assigned waves) GOTO print routine 400.

170 IF FLG(n) = 1 THEN 150 ELSE 180 ‘This wave has completed its transmission’.

180 IF t > TM(n) THEN 200 ELSE 150. ‘A wave has reached a termination or branch point’.

200 Increment m. ‘Calculate ...