I'm learning a "PHY full rate clock divider configuration register" and it represents its register Address as 16’b11_0_1_0nnn_0001_0011

I think 16 stands for bit number, 'b means binary, but what does _ and n mean here?

  • \$\begingroup\$ where does this information come from? \$\endgroup\$
    – jsotola
    Commented May 22, 2022 at 19:00

1 Answer 1


Looking at it, it's a 16 bit binary number. So that's what the 16'b must mean.

Underscore doesn't really mean anything. It's being used to split the groups of bits up for human readability.

"0nnn" is some binary number between 0000 and 0111. Read the rest of the documentation to work out what these numbers are for.

  • \$\begingroup\$ At a guess, the 0_1_0 is the expected value, but the three bits can be any combination and represent a field "nnn". As you say, the documentation needs to be consulted. \$\endgroup\$ Commented May 22, 2022 at 19:55
  • \$\begingroup\$ Presumably, the device has several (up to 8) PHY devices and there is a register for each. The bits in "nnn" select the register. \$\endgroup\$
    – DoxyLover
    Commented May 23, 2022 at 8:44

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