CHAPTER 3 CPU FUNCTION
User’s Manual U12688EJ4V0UM00
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3.4.6 External expansion mode
The V850E/MS1 allows external devices to be connected to the external memory space by using the pins of ports
4, 5, 6, A, and B. Setting the external expansion mode is carried out by selecting each pin of ports 4, 5, 6, A, and B in
the control mode by means of the MM register.
Note that the status at reset time differs as shown below in accordance with the operating mode specification set
by pins MODE0 to MODE3 (refer to 3.3 Operation Modes for details of the operation modes).
(1) Status at reset time in each operation mode
(a) In the case of ROM-less mode 0
At reset time, each pin of ports 4, 5, 6, A, and B enters the control mode, so the external expansion mode
is set without changing the MM register (the external data bus width is 16 bits).
(b) In the case of ROM-less mode 1
At reset time, each pin of ports 4, 5, 6, A, and B enters the control mode, so the external expansion mode
is set without changing the setting of the MM register (the external data bus width is 8 bits).
(c) In the case of single-chip mode 0
At reset time, since the internal ROM area is accessed, each pin of ports 4, 5, 6, A, and B enters the port
mode and external devices cannot be used.
Set the MM register to change to the external expansion mode.
(d) In the case of single-chip mode 1
Internal ROM area is allocated from address 100000H (Refer to 3.4.5 (1) (c) Internal ROM area
relocation function). For that reason, at reset time, each pin of ports 4, 5, 6, A, and B enters the control
mode, and is set in the external expansion mode without changing the settings of the MM register (the
external data bus width becomes 16 bits).
(2) Memory expansion mode register (MM)
This register sets the mode of each pin of ports 4, 5, 6, A, and B. In the external expansion mode, an external
device can be connected to an external memory area of up to 32 MB. However, an external device cannot be
connected to the internal RAM area, internal peripheral I/O area, and internal ROM area in the single-chip
modes 0, 1 (even if connected physically, it does not become an access target.).
The MM register can be read/written in 8- or 1-bit units. However, bits 4 to 7 are fixed to 0.
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