Update:

I received the following information from a helpful reader:

The Module is a self controlled Backup Memory and a Real Time Clock. The two NEC D444s are not Watchdogs, but Static RAM (Memory). Both the RAM and the RTC need very low power, which is provided by the Goldcap 1,0 Farad Condenser for several weeks. The Memory Control (Adressing and Chip Select) is provided by the 8255 which gives three times 8 bit ports. One for adresses, the second for data, the third for control of RAM and RTC. Only RTC and RAM is held on power by the Goldcap, while 8255 and the main computer (host) may be switched off (for example during power fail or by will). The 8255 is used to save adress room. The Module itself is around mid nineteen-eighties.