How can I calculate the value series termination resistors? How accurately can the resistance value be calculated. Are 1% resistors required?
High speed signals make signal simulation a valuable tool. If signal integrity simulation is not practical the current and voltage graphs in the datasheet can be used to approximate typical output driver impedance. The output impedance plus a series resistor near the output should match the impedance of the signal trace on the printed circuit board. In most applications it is only practical to match output and trace impedance to the nearest 30%. 1% resistors are not required.
More tips on Blackfin hardware design can be found in application note EE-281
To calculate the impedance of your signal traces, this might come in handy: http://web.awrcorp.com/Usa/Products/Optional-Products/TX-Line/ .
I use the following equation to calculate the value of termination resistors;
Rs = Zo – Zout whereby Zout – output impedance of the transmitter; Zo – impedance of the trace.
I get output driver impedance (Zout) from ADSP datasheet (figure 37 page 51) approximately 30 Ohm. As I don’t know what type will be traces on my board (page 21 of EE-326) I assume Z0 = 50-60 Ohm. The value of termination resistor is in a range 20 – 30 Ohm. Are my calculations correct?
I am going to use this resistors to terminate D0-D7 between BF537 and MT48LC32MA2.
I have some questions like this:
1. What about serial termination of other signals SDARM (A1-A12, CLK, CKE, CS, RAS, CAS);
3. What about placement of terminate resistors? Where I must place it near BF or SDRAM?
2. What about serial termination between BF537 and Flash (AM29LV400B) (A0-A17, D0-D15, and control signals). Do these signals require termination too?
4. What about unused signals? Need I terminate them with pull down resistors?
5. What about serial termination CLKIN signal (BF537) and if it is necessary what value of resistor shall I choose?
6. Why I must pull down TRST (JTAG reset pin EE-68) but datasheet requires (This pin should be pulled low if the JTAG port is not used)?
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