Stc89c516rd single chip microcomputer contains 1280 bytes of RAM data memory, which is enough for general applications. However, due to the use of RTOS real-time multitasking operating system in the system, it needs to occupy part of ram, and a large amount of data needs to be stored. The generation of LCD interface also needs to occupy RAM space, so it is selected to expand 32K bytes of RAM data memory. The expanded data memory is completed by cy62256.

Extended memory circuit diagram design

Cy62256 is a 32kx8 bit static random access memory chip. A0 ~ A14 are on-chip 15 bit address lines, I / 0 ports are 8-bit bidirectional data lines, CE is chip selection signal (active at low level), 0e is read permission signal line (active at low level), and we is write signal line (active at low level). Cy62256 chip selection signal CE is connected to A15 bit of MCU. Cy62256 is 32K (215) ram and occupies 15 address lines. According to this connection, the decoding addresses of cy62256 are 0000H and efffh, a total of 32K. 74HC373 in Figure 3.6 is the address latch. Its function is to separate and lock the address signals in the time-sharing multiplexing port of the address / data bus of the single chip microcomputer for use by the extended data memory or program memory (the system has no extended program memory). Ale of MCU is a low 8-bit address latch control signal, which is connected to Le Pin of 74HC373 to enable 373 to latch address signal.

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