RSC4128 datasheet(16/49 Pages) ETC

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RSC-4128

Data Sheet

P/N 80-0206-J

Extended Address Register

0D2H R/W

ExtAdd

Bit [7:6]

(Unused)

Bit 5

cb1

MOVC reads/writes and processor fetches access addresses

00000H-0FFFFH of Constant/Code Space (Code Bank 0)

MOVC reads/writes and processor fetches access addresses

10000H-1FFFFH of Constant/Code Space (Code Bank 1)

Cleared on reset.

Bit 4

MOVX reads access Constant/Code Space

MOVX reads access Data Space

Cleared on reset.

Bits [3:0]

“eda” bits – extended address bits [19:16]

used by MOVX to generate addresses bits A[19:16] of Data and/or Constant/Code Space.

Cleared on reset.

The programming of the Extended Addressing Register(“extAdd”) is independent of whether the ROM is external or

internal. That is, an external ROM mirrors an internal ROM exactly. This allows products to be developed with

external ROM and masked with the same binary in an internal ROM part.

Note: Unlike the RSC-3x, the last 256 bytes of Data Space are not allocated for internal processor functions. All

internal processor functions are mapped to the SFR area of Register space, leaving all Data space addresses

potentially accessible as external memory.

There are 8 data bus lines. These pins are bi-directional: they are normally inputs except when there is an external

write to Code Space or Data Space. These pins, D[7:0], have weak pull-up devices (~100K ohm) to keep them

from floating when no device is driving the data bus.

External Memory Interface Control Signals

There are 4 active low read/write strobes for reading from and writing to external Constant/Code Space or Data

Space: -RDR, -WRC, -RDF, -WRD. To support cost effective software development for large memory spaces

the external memory strobes are different from earlier RSC chips. The –RDR signal replaces the previous –RDC

signal and the –RDF signal replaces the previous –RDD signal. The –XM pin replaces the previous –XML and

–XMH pins on earlier RSC devices. The –WRC signal and the –WRD signal are the same as in previous RSC

chips. (See “DC Characteristics” section for electrical characteristics.)

The 20-bit extended address for a memory-reference instruction or a code fetch may be directed to the internal

ROM, or it may be directed to an external ROM or flash. The address is always an external address if:

1) the instruction is MOVX read and the “rw” bit is set, or

2) the instruction is MOVX write, or

3) the –XM pin is low, or

4) the instruction is a MOVC write

Otherwise the address is internal.

The –XM pin is an active low input pin that disables internal ROM when pulled low, and forces the use of external

memory for Constant/Code Space. Write accesses to Constant/Code Space (MOVC write; –WRC active) are

always directed off-chip. The -XM pin has a weak pull-up device (~10K ohm) to enable the internal ROM when no

connection is made to this pin. At the end of reset -XM is sampled and, if pulled low externally, the internal 10K

ohm pull-up device is disabled.

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