HMC7044 GPIx Control

Question

HMC7044 datasheet specifies GPIx Control settings in registers 0x0046, 0x0047, 0x0048, 0x0049. It is given that the setting 0010 is to Select PLL1 reference manually, Bit 1. Also, it is specified that the next setting 0011 is to Select PLL1 reference manually, Bit 0. How can we manually select any of the four reference clocks using these two settings?

Thanks, 
 Aysha

emrecangidik · Accepted Answer

Hi Aysha, 
 HMC7044 has 4 general purpose inputs. To manually select active references between four reference inputs, you need to set the two GPI inputs for a 2-bit operation. 
 For example, when you set GPI registers 0x47 = 0x05, 0x46 = 0x07 for GPI0 and GPI1, reference selection truth table becomes as follows

GPI0 State 
 GPI1 State 
 Active Reference

LOW 
 LOW 
 CLKIN0

LOW 
 HIGH 
 CLKIN1

HIGH 
 LOW 
 CLKIN2

HIGH 
 HIGH 
 CLKIN3

Thanks, 
 Emrecan)

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HMC7044 GPIx Control