Hi Gene Parrott; Here's an example of the third step...
In these diagrams, time increases down the page. The transmission line is shown with the controller on the left, and
termination on the right, and with two RDRAM chips between them:
'C' = Controller
"-" = transmission line
'A' = RDRAM chip "A"
'B' = RDRAM chip "B"
'T' = Termination resistor
't' = Time
Time values are in ns. For convenience, I chose a time scale of 0.10ns per step, but that the third step does not depend on this selection will be obvious. (For the illustration shown, an actual bit time would be more like 20 steps or so. But since the 3rd step is an event that happens between one chip ceasing transmission and another chip turning on, its existence is not dependent on the time scale. It's duration, by the way, turns out to depend on how far apart the SDRAMs are, in ns.
Code:
'0' = 1.8V
'1' = 1.4V
'2' = 1.0V
'3' = 0.6V
Action, Read of a long series of one bits from "A"
t(ns) C---A------B----T
0.0 00001000000000000
0.1 00011100000000000
0.2 00111110000000000
0.3 01111111000000000
0.4 21111111100000000 Note: "A" arrives at controller at 0.4ns
0.5 22111111110000000
0.6 22211111111000000
0.7 22221111111100000
0.8 22222111111110000
0.9 22222211111111000
1.0 22222221111111100
1.1 22222222111111110
1.2 22222222211111111
1.3 22222222221111111
1.4 22222222222111111
1.5 22222222222211111
1.6 22222222222221111
1.7 22222222222222111
1.8 22222222222222211
1.9 22222222222222221
2.0 22222222222222222 Note: Bus reaches steady state
Action, "A" finishes reading a long series of ones
t(ns) C---A------B----T
0.00 22221222222222222
0.10 22211122222222222
0.20 22111112222222222
0.30 21111111222222222
0.40 01111111122222222 Note: "A" turn off arrives at controller at 0.4ns
0.50 00111111112222222
0.60 00011111111222222
0.70 00001111111122222
0.80 00000111111112222
0.90 00000011111111222
1.00 00000001111111122
1.10 00000000111111112
1.20 00000000011111111
1.30 00000000001111111
1.40 00000000000111111
1.50 00000000000011111
1.60 00000000000001111
1.70 00000000000000111
1.80 00000000000000011
1.90 00000000000000001
2.00 00000000000000000
Action: "B" begins reading a series of ones:
t(ns) C---A------B----T
0.00 00000000000100000
0.10 00000000001110000
0.20 00000000011111000
0.30 00000000111111100
0.40 00000001111111110
0.50 00000011111111111
0.60 00000111111111111
0.70 00001111111111111
0.80 00011111111111111
0.90 00111111111111111
1.00 01111111111111111
1.10 21111111111111111 Note: "B" arrives at C at 1.1ns
1.20 22111111111111111
1.30 22211111111111111
1.40 22221111111111111
1.50 22222111111111111
1.60 22222211111111111
1.70 22222221111111111
1.80 22222222111111111
1.90 22222222211111111
etc.
Since "B" arrives 0.7ns (= 1.1ns - 0.4ns) after "A" arrives, we must
start "A" 0.7ns later than "B" in order for their signals to arrive
with the same phase at the controller.
3-volt step case. "A" drives long series of ones to the controller, then
turns off and "B" takes over, driving a long series of ones.
Example. I choose to end "A"s output at its nominal 1.25ns time, and turn "B"
on at its nominal 1.25ns time. These times have to be converted to actual
times by adding delaying "A" by 0.70ns Therefore, "A" actually turns off at
time 1.95ns, while "B" actually turns on at 1.25ns.
This leads to the following result:
t(ns) C---A------B----T
1.15 22222222222222222 Note: "A" in steady state driving one
1.25 22222222222322222 Note: "B" begins driving one (3rd step)
1.35 22222222223332222
1.45 22222222233333222
1.55 22222222333333322
1.65 22222223333333332
1.75 22222233333333333
1.85 22222333333333333
1.95 22222333333333333 Note: "A" turns off output when
2.05 22222233333333333 3rd step "B" output reaches it.
2.15 22222223333333333
2.25 22222222333333333
2.35 22222222233333333 Note: C begins receiving one from "B"
2.45 22222222223333333
2.55 22222222222333333
2.65 22222222222233333
2.75 22222222222223333
2.85 22222222222222333
2.95 22222222222222233
3.05 22222222222222223
3.15 22222222222222222
-- Car
