GDC21D601 Datasheet, PDF (20/189 Pages) Hynix Semiconductor – 32-Bit RISC MCU

GDC21D601
3. System Decoder
The decoder in an AMBA system is used to perform a centralized address decoding function, which gives two
main advantages:
- It improves the portability of peripherals, by making them independent of the system memory map.
- It simplifies the design of bus slaves, by centralizing the address decoding and bus control functions.
The decoder performs three main tasks:
- address decoder
- default transfer response
- protection unit
The decoder generates a select signal for each slave on the ASB bus and, under certain circumstances, will not
select any slaves and provide the transac-tion response itself.
The MCU System Memory Map is shown in Figure 1.
The decoder greatly simplifies the slave interface and removes the need for the slave to understand the different
types of transfer that may occur on the bus.
4. Memory Map
The system decoder controls the memory map of the system and generates a slave select signal for each memory
region.
The ReMap signal is used to provide a different memory map: ROM is required at address 0 when power on reset,
and RAM also may be used at address 0 during normal operation.
The ReMap signal is typically provided by a Power Management Unit (PMU) which drives ReMap to LOW at
reset. The signal is only driven to HIGH after a particular register in the PMU is accessed (See Section. 9 Power
Management Unot for detail). When ReMap is HIGH and isram signal is HIGH, then Memory Map Configuration
is MODE A which the internal SRAM is located at address 0x00. And When ReMap is HIGH and drambank0
signal is HIGH, then Memory Map Configuration is Mode B which the DRAM bank #0 is located at address 0x00.
The isram and drambank0 signal come from MCU Controller. See Section 8. MCU Controller for detail.
Figure 2. Memory map configuration shows both the Reset (MODE R) and the Normal (MODE B and MODE A)
memory map
Figure 1. shows the system memory map.
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