# Oscillator connection

I have two questions here for how to connect the oscillator to a microcontroller (SPC584b):

1. How can I determine the values of the capacitors?
2. What is the need of SB2 & SB3?

• Normally this should be provided in the datasheet of the oscillator you want to use. There is a formula for that. – Swedgin Oct 31 '19 at 8:52
• SB1, SB2 and SB3 allows you to either supply your own clock (SB1 and SB3 closed, SB2 open) or to use the quartz as clock (SB1 and SB3 open, SB2 closed). – Wheatley Oct 31 '19 at 9:35

Using Solder Bridges SB1, SB2, SB3 you can select the configuration:

Use external clock (Ext_CLK):

SB1 = closed, SB2 = open, SB3 = closed (my guess, check the IC's datasheet).

Use crystal for oscillator:

SB1 = open, SB2 = closed, SB3 = open

The capacitors C1 and C2 are load capacitors they are needed to make the crystal oscillator work. Their value should be mentioned in the datasheet of the crystal X2.

If no load capacitor value is given start with C1 = C2 = 10 pF and see if that works.

• C1 and C2 are given on the schematic: 18pF each. I suppose OP is talking about some other capacitors but has not provided enough information. – Wheatley Oct 31 '19 at 9:42
• Thanks for your answer. Can i change to the external CLK by welding (SB3,SB1) and remove welding on SB2, on a board that already printed? – Basel Tahboub Oct 31 '19 at 13:39
• Welding? I hope you mean soldering! Yes you can remove or re-apply the solder bridge as you like. If they're small, good soldering skills are required. Maybe you need some desoldering braid for that: en.wikipedia.org/wiki/Desoldering If you have no experience with this and destroying your board means trouble: then practice your (de)soldering skills on a junk-PCB from some old unused equipement! on a board that already printed? You mean: "A board that is already populated (with components). – Bimpelrekkie Oct 31 '19 at 13:43
• Yes I mean soldering, Thanks a lot for your advice it make things clear to me. – Basel Tahboub Oct 31 '19 at 14:35