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Timings und voltages, nominal and real. The values you find in the text arereal world measurements. So thee might be slight differences between my measurements and what you fin when you do tests on your system. A real world value of 102 ms might be nominal (meant to be) 100 ms.
LSB und MSB We are used to numbers where the most significant digit is to the left. That is calld MSB order. LSB is just the opposite. The most significant digit is to the right. So MSB ordered 101110 is eqivalent to LSB ordered 011101. |
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Physical level The N-Digital System is a two wire system. just as all other current slot car systems. With an analog system the voltage betwee both wires is varied and the voltage change results in a rpm change of the motor and that in a speed change. Digital systems use a constant voltage between the wires, N-Digital uses 14V. As the voltage is not available as a control method for the speed, the cars mut be informed in a different way. And that different way are data packets that are sent over the same two wires, which are used to supply the energy for the cars. To transmit the data packets the 14V line ist switched on and off in a certain rhythm comparable to a morse code. The title image shows what it looks like. The data words are repeated every 5 ms that a frequency of 200 Hz. A detailed look reveals:
Each pulse has a duration of 50,8 µs. The duty cycle is nominally 3 : 1 or 1 : 3 depending on the logical value. On a logical 1 the lowphase has a nominal length of 12,7 µs and the highphase has a nominal length of 38,1 µs. Because of assymetries in the drivers the positive and negative pulses of the same length are .... not the same length, just close :) All data words are 16 bits long. Every datword starts with a lowphase. The bits are transferred in LSB order. The semantic data word in the image above is therefore 1111111111110001 or $FFF1 |
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Semantic level There is a checksum in all but one kind of data words. It consists of bits 8 to 11 in the semantic or bits 4 to 7 in the physical data word. In the following I will only use semantic data words. The data word ist split in 4 nibbles. Nibbles are chunks of 4 bits. The first nibble consits of bits 0..3. The third nibble (Bits 8..11) contains the checksum. It is calculated as $F - Nibble 0 - Nibble 1 - Nibble 3 ignoring overflows. data words are repeated in cycles. Each cycle consists of 3 data packets. A data packet consists of as many data words as hand controllers are connected to the powerbase plus 2. In each data packet the data from all controllers is sent. The id of cars/controllers starts with 1. When there is only one controller connected a data packet starts every 15 ms (6667 Hz) and the data from each controller is transmitted as often. When there are 8 controllers connected, the time per packet increases to 50 ms, so the frequency drops to 20 Hz. Each data packet starts with the data word $FFF1 or $FFD1, followed by the data words for each controller and at last an infoword. Theer are three different infowords and all three infowords together give the information to be displayed in Nincos tower. Each infoword is sent once in three consecutive cycles. Two of the infowords combined represent the number of laps and the third infoword givs the position of one car in the race. Because only every 3 Infoword is of this type and the position of 8 cars is transmittedt it will take 24 data pakets until all positions are send. When four controllers are connected this will be 24 * 6 data words, one every 5 ms resulting in 0,72 seconds. Startword: 1 1 1 1 1 1 1 1 1 1 L 1 0 0 0 1 Occurs at the start of every datapaket.
This word is send to set all cars on track to a given id.
Controllerword: 0 0 L T G3 G2 G1 G0 C3 C2 C1 C0 R3 R2 R1 R0 This word tells each car connected to the controller, what speed to use and whether the lane change button is pressed. Only packets for controllers which are connected to the powerbase are sent.
Lapword1: E3 E2 E1 E0 Z3 Z2 Z1 Z0 C3 C2 C1 C0 1 0 1 0 Number of laps to be displayed in the tower least significant digits.
Lapword2: H3 H2 H1 H0 T3 T2 T1 T0 C3 C2 C1 C0 1 0 1 1 Number of laps to be displayed in the tower most significant digits.
Positionword: C3 C2 C1 C0 R3 R2 R1 R0 C3 C2 C1 C0 1 1 0 0 Was auch Always vielleicht rennende Testen.
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Car id When a car reaches a deadstrip it does recognize the lower voltage. Now the car short circuits the two conductors in a special rhythm.
The rhythm depend on car id and state of the lane change button for the car. The lowphase (short circuit) tells you whether the button is pressed. The duration of the low phase is nominally 0.5 ms, when the button is not pressed. The duraition has a nominal length of 1 ms, when the button is pressed. The high phase (no short circuit) gives the cars id. It's duration is nominally 0.5 ms for car 1, 1 ms for car 2 and so on. Multilane extension Whenever a car passes a dead strip of the multiline extension, it will send a data packet of 3 bytes to the powerbase.
The data packet forms the string PX<CR>. The X is the cars id ored with $10 or $20 depending on the lane. The string is send as a serial data word using 1200 baud, 7 bits, no parity one stopbit.
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