p89v51rb2 NXP Semiconductors, p89v51rb2 Datasheet - Page 14

• Manufacturer Part Number: p89v51rb2
• Description: 8-bit 80c51 5 V Low Power 16/32/64 Kb Flash Microcontroller With 1 Kb Ram
• Manufacturer: NXP Semiconductors

NXP Semiconductors
P89V51RB2_RC2_RD2_4
Product data sheet
6.2.1 Flash program memory bank selection
6.2.2 Power-on reset code execution
6.2 Memory organization
The device has separate address spaces for program and data memory.
There are two internal flash memory blocks in the device. Block 0 has 16/32/64 kB and is
organized as 128/256/512 sectors, each sector consists of 128 B. Block 1 contains the
IAP/ISP routines and may be enabled such that it overlays the first 8 kB of the user code
memory. The overlay function is controlled by the combination of the Software Reset Bit
(SWR) at FCF.1 and the Bank Select Bit (BSEL) at FCF.0. The combination of these bits
and the memory source used for instructions is shown in
Table 5.
Access to the IAP routines in block 1 may be enabled by clearing the BSEL bit (FCF.0),
provided that the SWR bit (FCF.1) is cleared. Following a power-on sequence, the boot
code is automatically executed and attempts to auto baud to a host. If no auto baud
occurs within approximately 400 ms and the SoftICE flag is not set, control will be passed
to the user code. A software reset is used to accomplish this control transfer and as a
result the SWR bit will remain set. Therefore the user's code will need to clear the
SWR bit in order to access the IAP routines in block 1. However, caution must be
taken when dynamically changing the BSEL bit. Since this will cause different physical
memory to be mapped to the logical program address space, the user must avoid clearing
the BSEL bit when executing user code within the address range 0000H to 1FFFH.
At initial power up, the port pins will be in a random state until the oscillator has started
and the internal reset algorithm has weakly pulled all pins high. Powering up the device
without a valid reset could cause the MCU to start executing instructions from an
indeterminate location. Such undefined states may inadvertently corrupt the code in the
flash. A system reset will not affect the 1 kB of on-chip RAM while the device is running,
however, the contents of the on-chip RAM during power up are indeterminate.
When power is applied to the device, the RST pin must be held high long enough for the
oscillator to start up (usually several milliseconds for a low frequency crystal), in addition
to two machine cycles for a valid power-on reset. An example of a method to extend the
RST signal is to implement a RC circuit by connecting the RST pin to V
capacitor and to V
circuit is being used, provisions should be made to ensure the V
exceed 1 ms and the oscillator start-up time does not exceed 10 ms.
For a low frequency oscillator with slow start-up time the reset signal must be extended in
order to account for the slow start-up time. This method maintains the necessary
relationship between V
which may cause corruption in the code of the flash. The power-on detection is designed
SWR (FCF.1)
0
0
1
1
Code memory bank selection
SS
BSEL (FCF.0)
0
1
0
1
through an 8.2 k resistor as shown in
DD
Rev. 04 — 1 May 2007
and RST to avoid programming at an indeterminate location,
Addresses from 0000H to
1FFFH
bootcode (in block 1)
user code (in block 0)
P89V51RB2/RC2/RD2
8-bit microcontrollers with 80C51 core
Table
Figure
5.
Addresses above 1FFFH
user code (in block 0)
DD
rise time does not
5. Note that if an RC
DD
© NXP B.V. 2007. All rights reserved.
through a 10 F
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