The S7-200 is a micro block style PLC. Its really a replacement for the
series 95 CPUs.
The S7-300 is a totally different series of CPUs and I/O is more of an
The S7-200 and S7-300 lines are completely incompatible with each other and
use different programming software.
There is plenty of info on the Siemens website on both CPUs.
I've used S7-200's but never needed the clock. Here's a snipped from
the manual (should be available on the Siemens site -- happy hunting)
Read Real-Time Clock and Set Real-Time Clock
The Read Real-Time Clock (TODR) instruction reads the current
time and date from the hardware clock and loads it in an 8-byte
Time buffer starting at address T. The Set Real-Time Clock (TODW)
instruction writes the current time and date to the hardware clock,
beginning at the 8-byte Time buffer address specified by T.
You must code all date and time values in BCD format (for example,
16#97 for the year 1997). Figure 6-3 shows the format of the Time
The time-of-day (TOD) clock initializes the following date and time
after extended power outages or when memory has been lost:
Day of Week: Sunday
Error conditions that set ENO = 0
0006 (indirect address)
0007 (TOD data error) Set Real-Time Clock only
000C (clock not present)
Data Types: Byte
Operands: IB,QB, VB, MB, SMB, SB, LB, *VB, *LD, *AC
T Year: 00 to 99
T+1 Month: 01 to 12
T+2 Day: 01 to 31
T+3 Hours: 00 to 23
T+4 Minutes: 00 to 59
T+7 Day of Week: 0 to 7
The following is pasted from the .pdf:
The S7-200 CPU does not perform a check to verify that the day of
week is correct based upon the date. Invalid dates, such as
February 30, could be accepted. You should ensure that the date
you enter is correct.
Do not use the TODR/TODW instruction in both the main program and
in an interrupt routine. A TODR/TODW instruction in an interrupt
routine that attempts to execute while another TODR/TODW
instruction is in process cannot be executed. SM4.3 is set
indicating that two simultaneous accesses to the clock were
attempted (non-fatal error 0007).
The time-of-day clock in the S7-200 uses only the least
significant two digits for the year, so for the year 2000, the
year is represented as 00. The S7-200 PLC does not use the year
information in any way. However, user programs that use arithmetic
or compares with the year s value must take into account the
two-digit representation and the change in century.
Leap year is correctly handled through year 2096.
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.