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CHAPTER 3 CPU
3.8 Memory Access Mode
In the MB89950/950A series, the only memory access mode is the single-chip mode.
■ Single-chip mode
In single-chip mode, the device uses internal RAM and ROM only. Therefore, the CPU can access no areas
other than the internal I/O area, RAM area, and ROM area (internal access).
■ Mode pin (MODA)
Always set the mode pin, MODA, to V
SS
.
At reset, reads the mode data and reset vector from internal ROM.
Do not change the mode pin settings, even after completion of the reset (i.e. during normal operation).
Table 3.8-1 "Mode pin setting" lists the mode pin settings.
■ Mode data
Always set the mode data in internal ROM to "00
H
" to select single-chip mode.
Figure 3.8-1 Mode data structure
Table 3.8-1 Mode pin setting
MODA
pin state
Description
V
SS
Reads the mode data and reset vector from internal ROM.
V
CC
Prohibited settings
Bit 7 Bit 6Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Address
FFFD
H
Data Operation
00
H Selects single-chip mode.
Other than
00
H
Reserved. Do not set this value.