
CHAPTER 3 CPU FUNCTIONS
User’s Manual U12768EJ4V1UD
77
3.4.6
External expansion mode
The V850/SA1 allows external devices to be connected to the external memory space by using the pins of ports 4,
5, 6, and 9. To connect an external device, the port pins must be set to the external expansion mode by using the
memory expansion mode register (MM).
The address bus (A1 to A15) is set to multiplexed bus output with the data bus (D1 to D15), though separate bus
output is also possible by setting the memory address output mode register (MAM) (see IE-703017-MC-EMI User’s
Manual for debugging when using the separate bus).
Because the V850/SA1 is fixed to single-chip mode in the normal operation mode, the port/control mode alternate-
function pins enter the port mode, and the external memory cannot be used. When the external memory is used
(external expansion mode), specify the MM register or MAM register by the program (memory area is set by the MM
register).
(1) Memory expansion mode register (MM)
This register sets the mode of each pin of ports 4, 5, 6, and 9. In the external expansion mode, an external
device can be connected to an external memory area of up to 4 MB. However, an external device cannot be
connected to the internal RAM area, on-chip peripheral I/O area, and internal ROM area in the single-chip mode
(and even if the external device is connected physically, it cannot be accessed).
The MM register can be read/written in 8-bit or 1-bit units. However, bits 4 to 7 are fixed to 0.
After reset: 00H
R/W
Address: FFFFF04CH
Symbol
7
6
5
4
3
2
1
0
MM
0
MM3
MM2
MM1
MM0
MM3
P95 and P96 Operation Modes
0
Port mode
1
External expansion mode (HLDAK: P95, HLDRQ: P96)
MM2
MM1
MM0
Address Space
Port 4
Port 5
Port 6
Port 9
0
—
Port mode
0
1
64 KB
AD0 to
AD8 to
LBEN,
expansion mode
AD7
AD15
UBEN,
1
0
256 KB
A16,
R/W, DSTB,
expansion mode
A17
ASTB,
1
0
1
1 MB
A18,
WRL,
expansion mode
A19
WRH, RD
1
×
4 MB
A20,
expansion mode
A21
Other than above
RFU (reserved)
Caution
When switching to the external expansion mode, the P93 and P94 bits of port 9 (P9) must be set
to 1 before switching.
Remark
For details of the operation of each port pin, refer to 2.3 Description of Pin Functions.