These components are essential for the microcontroller's operation and are present in all Cortex-M-based systems. Joseph Yiu, in Definitive Guide to Arm® Cortex®-M23 and Cortex-M33 Processors, 2021 6.1.1 What is in the memory system?Īrm® Cortex®-M processors provide generic bus interfaces to allow memory blocks (e.g., SRAM, ROM, embedded flash) and peripherals to be connected to the processor. If non-volatile data storage is needed, the EEPROM size must also be checked. The number of variables and temporary data storage blocks required can be totaled when the program has been developed, perhaps adding an allowance for future expansion or changes to the specification. The remaining 128 registers are duplicates or unimplemented. The first 32 addresses in each bank are assigned as SFRs (total 128), but there are only 256 bytes in total of unique RAM locations (20h–7Fh, A0h–EFh and 120h–16Fh). For example, the 16F690 has four banks of 128 locations, equivalent to 512 addresses. Therefore, the total amount of RAM cannot simply be calculated as the number of locations per bank multiplied by the number of banks. Note that some blocks of RAM are unique, while others are common to all the RAM banks (that is, the same register is accessed at the corresponding address in different banks), while other address ranges may not be implemented at all. The file register RAM block, which includes the SRFs and GPRs, tends to increase in size with the program memory size and chip complexity, and ranges from 16 to 4096 bytes in the 8-bit PICs. ![]() Martin Bates, in PIC Microcontrollers (Third Edition), 2011 12.2.3 Data Memory
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