Communication memoryThe communication memory comprises a central battery-backed RAMin the PLC. It has three areas: 1) the communication flags (256 bytes),2) the semaphores (32), and 3) four memory pages.The communication flags are located in memory area F200H toF2FFH. The communication flags enable the cyclic interchange ofsmall volumes of data between the CPUs in the S5-135U/155U PLC.The four memory pages serve for the exchange of data blocks betweenCPUs.Please consult the Programming Guides of the CPUs to program thesetwo functions.The semaphores are used to coordinate the CPUs for access to thesame I/O address (see Programming Guides, operations SES andSEF).Addressing method for the page memory (vector register)The vector register serves to form subaddresses of several memoriesin a common address area. The register is an 8-bit register which iswritten to under address FEFFH. It cannot be read out.The page memory contains four pages of 1 Kbyte. An identificationnumber is assigned to each page. These are the numbers 252, 253,254 and 255.Pa g e M e m o r y f o rD a t a Bl o c k sVe c t o r R e g i s t e rf o r Pa g e Se l e c t i o n ,F a u l t R e g i s t e rSy n c h r o n i z a t i o nAr e a f o rO p e r a t i n g Sy s t e m sC o m m u n i c a t i o n F l a g sF EF F HF 7 F F HF 4 0 0 HF 3 0 0 HF 2 0 0 HPa g e N o .2 5 3 Pa g e N o .2 5 4Pa g e N o .2 5 5Pa g e N o .2 5 2Figure 6-8 Areas of the Communication Memory on the S5 Bus6923C Coordinator ModuleSystem ManualC79000-B8576-C199-03 6 - 23
