About dcf77code

dcfcode is a simple command-line utility that aims to produce (and decipher, too) strings of bits put together in accordance to DCF77 Timecode specification.

What for?

There does exist hardware capable of making radiowaves using these strings of bits as source of modulation, thus data created by this utility may be fed into Radio Controlled Clocks.

Features

• Produced timecode depends on localtime (not UTC), thus the DST flag of localtime drives selection of Z1/Z2 bits of timecode.

Bugs

• There is no way to set 'leap second' flag of timecode.
• Summer time announcement (A1) prediction depends on the change of DST flag of localtime.

Definitions

Timecode spans 60 bits. Within this project the timecode is represented as 8-byte chunk of data, which also has a local name -- a block.

Examples

By default, a timecode is created for current time:

% dcfcode -c
0000D2B86A2A5D00
% date
Tue Sep 26 15:46:35 EEST 2017

To decipher timecode contents, run:

% dcfcode -d 0000D2B86A2A5D00
0000D2B86A2A5D00 -> Tue Sep 26 15:46:00 2017 (MSD)

Note: DCF77 timecode is originally defined for Central European Time and carries no timezone information as such.

It's possible to define offset in minutes from current time (watch inner call of dcfcode):

% dcfcode -d `dcfcode -c -s +3`
000032B96A2A5D00 -> Tue Sep 26 15:49:00 2017 (MSD)

It's possible to produce multiple blocks (timecodes) at once:

% dcfcode -d `dcfcode -c -n 4`
0000D2B86A2A5D00 -> Tue Sep 26 15:46:00 2017 (MSD)
0000F2A86A2A5D00 -> Tue Sep 26 15:47:00 2017 (MSD)
000012A96A2A5D00 -> Tue Sep 26 15:48:00 2017 (MSD)
000032B96A2A5D00 -> Tue Sep 26 15:49:00 2017 (MSD)

It's possible partially or fully redefine current timestamp (for instance: lets set hour and minute to 22:33 while leaving year, month, day of month at their defaults (at the moment of this writing)):

% dcfcode -d `dcfcode -c -t 2233`
00007246642A5D00 -> Tue Sep 26 22:33:00 2017 (MSD)

And it is possible to use a block as a timestamp:

% dcfcode -c -t 0000D2B86A2A5D00 -s +1 -n 2
0000F2A86A2A5D00
000012A96A2A5D00
% dcfcode -d 0000D2B86A2A5D00 0000F2A86A2A5D00 000012A96A2A5D00
0000D2B86A2A5D00 -> Tue Sep 26 15:46:00 2017 (MSD)
0000F2A86A2A5D00 -> Tue Sep 26 15:47:00 2017 (MSD)
000012A96A2A5D00 -> Tue Sep 26 15:48:00 2017 (MSD)

Digging into timecode:

% dcfcode -D 0000D2B86A2A5D00
# 0000D2B86A2A5D00
             0 :    0 : M       : Start of minute
00000000000000 :    0 : weather : Weather info
             0 :    0 : R       : Abnormal transmitter operation
             0 :    0 : A1      : Summer time announcement
             1 :    1 : Z1      : CEST in effect
             0 :    0 : Z2      : CET in effect
             0 :    0 : A2      : Leap second announcement
             1 :    1 : S       : Start of encoded time
       0110001 :   46 : min     : Minutes 00-59
             1 :    1 : P1      : Even parity over minute bits
        101010 :   15 : hour    : Hours 00-23
             1 :    1 : P2      : Even parity over hour bits
        011001 :   26 : dom     : Day of month
           010 :    2 : dow     : Day of week (Mon=1, Sun=7)
         10010 :    9 : month   : Month number 01-12
      11101000 :   17 : year    : Year within century 00-99
             0 :    0 : P3      : Parity over date bits
             0 :    0 : -       : Minute Mark (no AM)

There are two counter-intuitive things in the output shown above: 1. binary values in the first column have their least significant bit on the left; 2. don't try to convert multibit fields to decimal form directly, as they are BCD-encoded numbers and are easily interpreted when stated in hex form. Lets read, for instance, day of month field:

(lsb)011001 -{reversed}-> 100110(lsb) -{padded with zeros}-> 0010 0110 -{as hex}-> 26h.

Encoding Details

Sixty bits of the DCF77 timecode are laid down into 7+0.5 bytes of the block (lsb first):

• Bit 0 of DCF77 timecode corresponds to (byte 0, bit 0) of the block;
• Bit 1 of DCF77 timecode -> (byte 0, bit 1) of the block;
• ...
• Bit 59 -> (byte 7, bit 3) of the block.