ST9291 ST Microelectronics, ST9291 Datasheet - Page 18

• Manufacturer Part Number: ST9291
• Description: 16-48K ROM HCMOS MCU WITH ON SCREEN DISPLAY AND VOLTAGE TUNINGOUTPUT
• Manufacturer: ST Microelectronics

ST9291
1.2.1 INTRODUCTION
The memory of the ST9291 is functionally divided
into two areas, the Register File and Memory. The
Memory may optionallybe divided into two spaces,
Program Memory for Program code and Data
Memory for Data.
The memory spaces are selected by the execution
of the SDM and SPM instructions (Set Data Mem-
ory and Set Program Memory, respectively). There
is no need to use either of these instructions again
until the memory area required is to be changed.
1.2.1.1 Program Space
The Program memory space of the ST9291 con-
sists of 48K bytes of on-chip ROM (addressed from
0 to BFFF) and 640 bytes of on-chip RAM (ad-
dressed from FD80h to FFFFh); refer to the mem-
ory map tables and drawing on the following page
for the memory mapping for other ROM sizes. The
first 256 memory locations from address 0 to
00FFh (hexadecimal) hold the Reset Vector, the
Top-Level (Pseudo Non-Maskable) interrupt, the
Divide by Zero Trap vector and, optionally, the
interrupt vector table for use with the on-chip
18/20
peripherals and the external interrupt sources.
Each vector is contained in two consecutive byte
locations, the high order address held in the lower
(even) byte, the low order address held in the up-
per (odd) byte, forming the address which is
loaded into the Program Counter when selected
by the interrupt vector provided by the interrupt
source. This should point to the relevant Interrupt
Service routine provided by the User for immedi-
ate response to the interrupt.
1.2.1.2 Data Space
The ST9291 addresses the 640 bytes of on-chip
RAM memory from addresses FD80h to FFFFh in
both Program and Data Space. On-chip general
purpose Registers may be used as additional RAM
memory for minimum chip count systems.
The Data Space is selected by the execution of
the SDM instruction. All subsequ ent memory ref-
erences will access the Data Space. When a
separate Data Space is not required, data may
stored in RAM or ROM memory within the Pro-
gram Space.