Step7: Read a serial signal via IO

Format of the SAT time string
The SAT time string is a sequence of 29 ASCII characters starting with the STX
(start-of-text) character and ending with the ETX (end-of-text) character. The format
is:
<STX>tt.mm.jj/w/hh.mm.ssMEzzxy<CR><LF><ETX>
The letters printed in italics are replaced by ASCII numbers whereas the other
characters are part of the time string. The groups of characters as defined below:
<STX> Start-Of-Text (ASCII code 02h)
dd.mm.yy the current date:
dd day of month (01..31)
mm month (01..12)
yy year of the century (00..99)
w the day of the week (1..7, 1 = Monday)
hh.mm.ss the current time:
hh hours (00..23)
mm minutes (00..59)
ss seconds (00..59, or 60 while leap second)
zz time zone indicator:
‘Z ‘ MEZ European Standard Time, daylight saving disabled
‘SZ’ MESZ European Summertime, daylight saving enabled
x clock status characters:
‘*’ DCF77 clock currently runs on XTAL
GPS receiver has not checked its position
‘ ‘ (space, 20h) DCF77 clock is sync'd with transmitter
GPS receiver has determined its position
y anouncement of discontinuity of time, enabled during last hour
before discontinuity comes in effect:
‘!’ announcement of start or end of daylight saving time
‘ ‘ (space, 20h) nothing announced
<CR> Carriage return (ASCII code 0Dh)
<LF> Line feed (ASCII code 0Ah)
<ETX> End-Of-Text (ASCII code 03h)