Internal Memory Size Select Register (Ims) - NEC uPD78F4225Y Manual

5. INTERNAL MEMORY SIZE SELECT REGISTER (IMS)

The IMS is a register that prevents by software a part of the internal memory from being used. By using this
register, the memory of the µ PD78F4225Y can be mapped in the same manner as a mask ROM model with different
internal memory (ROM and RAM) capacity.
This register is set by using an 8-bit memory manipulation instruction.
Its value is set to FFH by RESET input.
Figure 5-1. Format of Internal Memory Size Select Register (IMS)
Address: 0FFFCH
7
1
IMS
IMS is not provided on the mask ROM models ( µ PD784224Y and 784225Y).
Caution
The value to be set to the IMS to map the memory of the µ PD78F4225Y in the same manner as the mask ROM
model is shown in Table 5-1.
Table 5-1. Set Value of Internal Memory Size Select Register (IMS)
16
At reset: FFH W
6 5 4
1 ROM1 ROM0
ROM1 ROM0
0 0 48K bytes
0 1 64K bytes
1
0 96K bytes
1 1 128K bytes
RAM1 RAM0
0 0 1536 bytes
0 1 2304 bytes
1 0 3072 bytes
1 1 3840 bytes
Mask ROM Model
µ PD784225Y
µ PD784226Y
3 2 1
1 1 RAM1
Selects internal ROM capacity
Selects peripheral RAM capacity
Set Value of IMS
EEH
FFH
µ PD78F4225Y
0
RAM0