ADUC7023 Analog Devices, ADUC7023 Datasheet - Page 40

• Manufacturer Part Number: ADUC7023
• Description: Precision Analog Microcontroller, 12-Bit Analog I/O, ARM7TDMI MCU
• Manufacturer: Analog Devices

Specifications of ADUC7023

• Mcu Core: ARM7 TDMI
• Mcu Speed (mips): 40
• Sram (bytes): 8192Bytes
• Gpio Pins: 20
• Adc # Channels: 12
• Other: PWM

ADuC7023
EXECUTION TIME FROM SRAM AND FLASH/EE
Execution from SRAM
Fetching instructions from SRAM takes one clock cycle because
the access time of the SRAM is 2 ns, and a clock cycle is 22 ns
minimum. However, if the instruction involves reading or
writing data to memory, one extra cycle must be added if the
data is in SRAM (or three cycles if the data is in Flash/EE); one
cycle to execute the instruction and two cycles to obtain the
32-bit data from Flash/EE. A control flow instruction (a branch
instruction, for example) takes one cycle to fetch but also takes
two cycles to fill the pipeline with the new instructions.
Execution from Flash/EE
Because the Flash/EE width is 16 bits and the access time for
16-bit words is 22 ns, execution from Flash/EE cannot be
completed in one cycle (as can be done from SRAM when the
CD bit = 0). Also, some dead times are needed before accessing
data for any value of CD bits.
In ARM mode, where instructions are 32 bits, two cycles are
needed to fetch any instruction when CD = 0. In thumb mode,
where instructions are 16 bits, one cycle is needed to fetch any
instruction.
Timing is identical in both modes when executing instructions
that involve using the Flash/EE for data memory. If the instruction
to be executed is a control flow instruction, an extra cycle is
needed to decode the new address of the program counter, and
then four cycles are needed to fill the pipeline. A data processing
instruction involving only the core register does not require any
extra clock cycles. However, if it involves data in Flash/EE, an
extra clock cycle is needed to decode the address of the data,
and two cycles are needed to get the 32-bit data from Flash/EE.
An extra cycle must also be added before fetching another
instruction. Data transfer instructions are more complex and
are summarized in Table 34.
Table 34. Execution Cycles in ARM/Thumb Mode
Instructions
LD
LDH
LDM/PUSH
STR
STRH
STRM/POP
1
2
The SWAP instruction combines an LD and STR instruction with only one
N is the number of data to load or store in the multiple load/store instruction
(1 < N ≤ 16).
fetch, giving a total of eight cycles + 40 ns.
1
1
Fetch
Cycles
2/1
2/1
2/1
2/1
2/1
2/1
1
N
Dead
Time
1
1
N
1
2
1
Data Access
2
1
2 × N
2 × 20 ns
20 ns
2 × N × 20 ns
2
1
Dead
Time
1
1
N
1
1
N
1
1
Rev. B | Page 40 of 96
RESET AND REMAP
The ARM exception vectors are all situated at the bottom of the
memory array, from Address 0x00000000 to Address 0x00000020
as shown in Figure 31.
By default, and after any reset, the Flash/EE is mirrored at the
bottom of the memory array. The remap function allows the
programmer to mirror the SRAM at the bottom of the memory
array, which facilitates execution of exception routines from
SRAM instead of from Flash/EE. This means exceptions are
executed twice as fast, being executed in 32-bit ARM mode with
32-bit wide SRAM instead of 16-bit wide Flash/EE memory.
Remap Operation
When a reset occurs on the ADuC7023, execution automatically
starts in factory programmed, internal configuration code. This
kernel is hidden and cannot be accessed by user code. If the part is
in normal mode (BM pin is high), it executes the power-on
configuration routine of the kernel and then jumps to the reset
vector address, 0x00000000, to execute the reset exception
routine of the user.
Because the Flash/EE is mirrored at the bottom of the memory
array at reset, the reset interrupt routine must always be written
in Flash/EE.
The remap is done from Flash/EE by setting Bit 0 of the Remap
register. Caution must be taken to execute this command from
Flash/EE above Address 0x00080020, and not from the bottom
of the array because this is replaced by the SRAM.
This operation is reversible. The Flash/EE can be remapped at
Address 0x00000000 by clearing Bit 0 of the Remap MMR.
Caution must again be taken to execute the remap function
from outside the mirrored area. Any type of reset remaps the
Flash/EE memory at the bottom of the array.
KERNEL
INTERRUPT
SERVICE ROUTINES
INTERRUPT
SERVICE ROUTINES
ARM EXCEPTION
VECTOR ADDRESSES
Figure 31. Remap for Exception Execution
0x00000020
0x00000000 0x00000000
0x00080000
0x00010000
0xFFFFFFFF
0x0008FFFF
0x00011FFF
FLASH/EE
SRAM
MIRROR SPACE