Maxim Integrated Secure Microcontroller - Manual (Page 27)

Secure Microcontroller User’s Guide
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Figure 4-5. Nonpartitionable Memory Map for DS5001/DS5002 Series
4.5 DS5001/DS5002 Memory-Mapped Peripherals
The DS5001FP and DS5002FP provide four peripheral chip enables (
PE4–PE1) designed to access
unencrypted peripherals on the bytewide bus. While PES = 1, all MOVX-based instructions present
unencrypted address and data on the bytewide bus. During these instructions the device asserts peripheral
chip-enable signals instead of the standard chip-enable signals based on the logical address. The
peripheral chip enables are decoded on 16kB boundaries, as shown in
Figure 4-6 . The PES bit operates
the same way in both partitionable and nonpartitionable modes.
The peripheral enables interfaced to battery-backed and nonbattery-backed peripherals. The lowest two
peripheral enables,
PE1 and PE2, are battery backed by the DS5001/DS5002. This means that when V
CC
is removed, the device drives these chip enables to a logic high inactive state. These signals should be
interfaced to SRAM and other devices that are battery backed. The upper two peripheral enables,
PE3 and
PE4, are not battery backed by the DS5001/DS5002. This means that when V
CC
is removed, the device
allows these signals to float to an undefined state. These signals should be interfaced to ADCs, UARTs,
and any other peripheral that is powered by V
CC
rather than V
CCO
.
A novel use of the PES signals is to double the available MOVX memory space. When set, the PES bit in
essence creates an overlay of 64kB, using the same MOVX addresses. By toggling the PES bit on and off,
the device can access up to 128kB of MOVX memory.
On occasion, a memory-mapped peripheral is needed that interfaces directly to an 8051 multiplexed bus.
When this occurs, MOVX instructions can be forced to use the expanded bus in any mode with the EXBS
bit (RPCTL.5). Setting this bit to logic 1 forces all MOVX instructions to the expanded bus. While EXBS
BYTEWIDE
BUS ACCESS
BYTEWIDE
BUS ACCESS
FFFFh
7FFFh
0000
64kB
32kB
PROGRAM
MEMORY
DATA
MEMORY
PROGRAM
RANGE
DATA
RANGE
PES=0
= BYTEWIDE ACCESS
(NV RAM)
= EXPANDED BUS ACCESS ON PORTS 0 AND 2