P89LV51RB2_RC2_RD2_5 © NXP B.V. 2009. All rights reserved.
Product data sheet Rev. 05 — 15 December 2009 14 of 76
NXP Semiconductors
P89LV51RB2/RC2/RD2
8-bit microcontrollers with 80C51 core
6.2 Memory organization
The device has separate address spaces for program and data memory.
6.2.1 Flash program memory bank selection
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 autobaud to a host. If no autobaud 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.
6.2.2 Power-on reset code execution
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
DD
through a 10 µF
capacitor and to V
SS
through an 8.2 kΩ resistor as shown in Figure 4. Note that if an RC
circuit is used, provision should be made to ensure the V
DD
rise time does not 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
DD
and RST to avoid programming at an indeterminate location,
which may cause corruption in the Flash code. The power-on detection is designed to
Table 5. Code memory bank selection
SWR (FCF.1) BSEL (FCF.0) Addresses from
0000H to 1FFFH
Addresses above
1FFFH
0 0 boot code (in block 1) user code (in block 0)
0 1 user code (in block 0)
10
11
