UPD78C18 datasheet(19/110 Pages) NEC

19 / 110 page

µPD78C17,78C18

2.4

MEMORY

The

µPD78C17 and 78C18 can address a maximum of 64 Kbytes of memory. The memory maps are shown in

Figs. 2-3 and 2-4. The external memory area and the internal RAM area can be freely used as program memory

and data memory. Because the access timing for internal memory and external memory are the same, pro-

cessing can be executed at high speeds.

(a)

Interrupt start addresses

The interrupt start addresses are all fixed as follows:

NMI ....................... 0004H

INTT0/INTT1 ......... 0008H

INT1/INT2 ............. 0010H

INTE0/INTE1 ......... 0018H

INTEIN/INTAD ...... 0020H

INTSR/INTST ........ 0028H

SOFTI .................... 0060H

(b) Call address table

The call address of a 1-byte call instruction (CALT) can be stored in the 64-byte area (for 32 call ad-

dresses) from address 0080H to address 00BFH.

(c)

Specific memory area

The reset start address, interrupt start addresses, and the call table are allocated to addresses 0000H to

00BFH, and this area takes account of these in use. Addresses 0800H to 0FFFH are directly addressable by

a 2-byte call instruction (CALF).

The

µPD78C18 has on-chip mask programmable ROM in addresses 0000H to 7FFFH.

(d) Internal data memory area

1-Kbyte RAM is incorporated in addresses FC00H to FFFFH. The RAM contents are retained for 1-Kbyte

internal data memory area in standby operation.

(e)

External memory area

With the

µPD78C17, the external memory can be expanded in steps in 63-Kbyte area (0000H to FBFFH)

by setting the MODE0 and MODE1 pins (see Table 2-3).

With the

µPD78C18, the external memory can be expanded in steps in 31-Kbyte area (8000H to FBFFH)

by setting the MEMORY MAPPING register (see Fig. 2-13).

The external memory is accessed using AD7 to AD0 (multiplexed address/data bus), AB7 to AB0 (ad-

dress bus), and the RD, WR, and ALE signals. Both programs and data can be stored in the external

memory.

(f) Working register area

A 256-byte working register area can be set in any memory location (specified by the V register) and

working register addressing is possible.

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