IS80C51 Datasheet, PDF (7/43 Pages) Integrated Silicon Solution, Inc – CMOS SINGLE CHIP 8-BIT MICROCONTROLLER

IS80C51
IS80C31
ISSI ^®
OPERATING DESCRIPTION
The detail description of the IS80C51/31 included in this
description are:
• Memory Map and Registers
• Timer/Counters
• Serial Interface
• Interrupt System
• Other Information
MEMORY MAP AND REGISTERS
Memory
The IS80C51/31 has separate address spaces for program
and data memory. The program and data memory can be
up to 64K bytes long. The lower 4K program memory can
reside on-chip. (IS80C51 only) Figure 5 shows a map of
the IS80C51/31 program and data memory.
The IS80C51/31 has 128 bytes of on-chip RAM, plus
numbers of special function registers. The lower 128 bytes
can be accessed either by direct addressing or by indirect
addressing. Figure 6 shows internal data memory
organization and SFR Memory Map.
The lower 128 bytes of RAM can be divided into three
segments as listed below and shown in Figure 7.
1. Register Banks 0-3: locations 00H through 1FH
(32 bytes). The device after reset defaults to register
bank 0. To use the other register banks, the user
must select them in software. Each register bank
contains eight 1-byte registers R0-R7. Reset initial-
izes the stack point to location 07H, and is incremented
once to start from 08H, which is the first register of the
second register bank.
2. Bit Addressable Area: 16 bytes have been as-
signed for this segment 20H-2FH. Each one of the
128 bits of this segment can be directly addressed (0-
7FH). Each of the 16 bytes in this segment can also
be addressed as a byte.
3. Scratch Pad Area: 30H-7FH are available to the
user as data RAM. However, if the data pointer has
been initialized to this area, enough bytes should be
left aside to prevent SP data destruction.
Program Memory
(Read Only)
FFFFH:
64K
Data Memory
(Read/Write)
FFFFH
External
External
EA = 0
External
0FFFH:
4K
0000
EA = 1
Internal
PSEN
Internal
FFH
7FH
80H
00
0000
RD WR
Figure 5. IS80C51/31 Program and Data Memory Structure
Integrated Silicon Solution, Inc. — 1-800-379-4774
7
MC003-1D
11/19/98