DS2251T_06 DALLAS [Dallas Semiconductor], DS2251T_06 Datasheet - Page 6

• Manufacturer Part Number: DS2251T_06
• Description: 128k Soft Microcontroller Module
• Manufacturer: DALLAS [Dallas Semiconductor]

INSTRUCTION SET
The DS2251T executes an instruction set that is object code compatible with the industry standard 8051
microcontroller. As a result, software development packages such as assemblers and compilers that have
been written for the 8051 are compatible with the DS2251T.
A complete description of the instruction set and operation are provided in the Secure Microcontroller
User’s Guide.
MEMORY ORGANIZATION
Figure 2 illustrates the memory map accessed by the DS2251T. The entire 64k of program and 64k of
data are available to the byte-wide bus. This preserves the I/O ports for application use. The user controls
the portion of memory that is actually mapped to the byte-wide bus by selecting the Program Range and
Data Range. Any area not mapped into the NV RAM is reached via the Expanded bus on Ports 0 and 2.
An alternate configuration allows dynamic Partitioning of a 64k space as shown in Figure 3. Selecting
PES = 1 provides access to the real-time clock on the DS2251T and enables
access as shown in Figure 4. These selections are made using Special Function Registers. The memory
map and its controls are covered in detail in the Secure Microcontroller User’s Guide.
PIN
71
65
55
68
69
70
has fallen below the V
DS2251T will drive this pin to a logic 0. Because the micro is lithium backed, this signal is
guaranteed even when V
low externally. This allows multiple parts to synchronize their power-down resets.
It corresponds to V
even when V
input.
connected to a micro interrupt input.
input.
SQW. Square-wave output from the DS1283 real-time clock. Can be programmed to output
a 1024Hz square wave.
INTB
INTP
INTA
VRST
PF
. This output goes to a logic 0 to indicate that the micro has switched to lithium backup.
.
.
.
. This I/O pin (open-drain with internal pullup) indicates that the power supply (V
INTP
INTA
INTB
from the real-time clock. This open-drain output requires a pullup and may be
from the real-time clock. This output may be connected to a micro interrupt
CC
from the real-time clock. This output may be connected to a micro interrupt
= 0V.
CC
< V
CCMIN
CC
LI
. Because the micro is lithium backed, this signal is guaranteed
= 0V. Because it is an I/O pin, it will also force a reset if pulled
level and the micro is in a reset state. When this occurs, the
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DESCRIPTION
PE3
and
PE4
for peripheral
CC
)