Memory Access Modes - Fujitsu F2MC-8L MB89620 Series Hardware Manual

8
3.

Memory Access Modes

The MB89620 series has three memory access modes:
• Single-chip mode
• External ROM mode
• Internal ROM/external bus mode
The CPU selects the memory access mode as part of the reset operation. In single-
chip mode, port 0, port 1, and port 2 function as I/O ports.
In external ROM mode or internal ROM/external bus mode, as port 0, port 1, and port 2
function as the external bus pins, external bus mode is enabled.
In external bus mode, memory and peripheral functions in external areas can be
accessed via the external bus operation. External bus operation also supports a ready
function and a hold function.
n Single-chip Mode
In single-chip mode, the device uses internal RAM and ROM only. Therefore, port 0 and port 1
can be used as general-purpose I/O ports and port 2 can be used as an output-only port.
Check: External ROM mode and internal ROM/external bus mode are not available on products that
n External ROM Mode
External bus mode is enabled in external ROM mode and the internal ROM area is
disconnected to become an external area. External memory and other devices are accessed
using the external bus.
n Internal ROM/External Bus Mode
External bus mode is enabled in internal ROM/external bus mode. Only external areas are
available via external access.
n External Bus Mode
When external ROM mode or internal ROM/external bus mode is selected, port 0 and port 1
function as the external bus pins for address and data I/O. The port 2 function as the external
bus control pins.
The ready function is provided to extend the bus cycle to access low-speed external memory or
peripheral functions.
A subset of pins (P20/BUFC to P22/HRQ) can be switched between acting as I/O pins or as
external bus control pins by setting the external bus pin control register (BCTR). The hold
function, which releases the external bus from the CPU, is available if P21/HAK and P22/HRQ
are used as external bus control pins.
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CHAPTER 3 CPU
support single-chip mode only. Similarly, single-chip mode and internal ROM/external bus mode
are not available on products that use external ROM only. For details, see Section 3.1, "Memory
Space."
External bus mode
MB89620 series