SAPI-S7 Write a single bit

This does not clarify much, the problem is perhaps general.

I can do stuff like this:
DB400,DINT12,1 both read and write, not problem.

But there is nothing like
DB400,BIT12.1,1

Readint bits I had solved, this is just bit banging, but writing then requires reading the byte to the PLC, manipulate the bit, and write the byte back - which is a potential error, since the PLC might update other bits in the byte after I have read, and these would then be overwritten by my "updated" byte.

How do I do bit manipulation in a DB ?


DATA_BLOCK "Handsha"
TITLE =PLC-PC
//
FAMILY : PVE
NAME : Dialog
VERSION : 0.1

STRUCT
PLC_TestAktiv : BOOL ;//False = Test stoppet True = Test i gang værende
PLC_TestOK : BOOL ;//False = Intet testresultat endnu True = Test afsluttet med OK-resultat

Any chance the request could use naming "Handsha" instead of DB203 in this case.

Regards
Jes Ramsing