P89V51RB2_09 Datasheet, PDF (16/80 Pages) NXP Semiconductors – 8-bit 80C51 5 V low power 16/32/64 kB flash microcontroller with 1 kB RAM

NXP Semiconductors
P89V51RB2/RC2/RD2
8-bit microcontrollers with 80C51 core
V_DD must stay below V_BOD at least four oscillator clock periods before the brownout
detection circuit will respond.
Brownout interrupt can be enabled by setting the EBO bit (IEA.3). If EBO bit is set and a
brownout condition occurs, a brownout interrupt will be generated to execute the program
at location 004BH. It is required that the EBO bit be cleared by software after the brownout
interrupt is serviced. Clearing EBO bit when the brownout condition is active will properly
reset the device. If brownout interrupt is not enabled, a brownout condition will reset the
program to resume execution at location 0000H. A brownout detect reset will clear the
BSEL bit (FCF.0) but will not change the SWR bit (FCF.1) and therefore will not change the
banking of the lower 8 kB of user code memory space.
6.2.5 Watchdog reset
Like a brownout detect reset, the watchdog timer reset will clear the BSEL bit (FCF.0) but
will not change the SWR bit (FCF.1) and therefore will not change the banking of the lower
8 kB of user code memory space.
The state of the SWR and BSEL bits after different types of resets is shown in Table 6.
This results in the code memory bank selections as shown.
Table 6. Effects of reset sources on bank selection
Reset source
SWR bit result BSEL bit result
(FCF.1)
(FCF.0)
External reset
0
0
Power-on reset
Watchdog reset
x
0
Brownout detect reset
Software reset
1
0
Addresses from 0000H to
1FFFH
Boot code (in block 1)
Addresses above
1FFFH
User code (in block 0)
Retains state of SWR bit. If SWR,
BSEL = 00 then uses boot code.
If SWR, BSEL = 10 then uses
user code.
User code (in block 0)
6.2.6 Data RAM memory
The data RAM has 1024 B of internal memory. The device can also address up to 64 kB
for external data memory.
6.2.7 Expanded data RAM addressing
The P89V51RB2/RC2/RD2 has 1 kB of RAM. See Figure 6 “Internal and external data
memory structure” on page 19.
The device has four sections of internal data memory:
1. The lower 128 B of RAM (00H to 7FH) are directly and indirectly addressable.
2. The higher 128 B of RAM (80H to FFH) are indirectly addressable.
3. The special function registers (80H to FFH) are directly addressable only.
4. The expanded RAM of 768 B (00H to 2FFH) is indirectly addressable by the move
external instruction (MOVX) and clearing the EXTRAM bit (see ‘Auxiliary function
Register’ (AUXR) in Table 4 “Special function registers” on page 11).
P89V51RB2_RC2_RD2_5
Product data sheet
Since the upper 128 B occupy the same addresses as the SFRs, the RAM must be
accessed indirectly. The RAM and SFRs space are physically separate even though they
have the same addresses.
Rev. 05 — 12 November 2009
© NXP B.V. 2009. All rights reserved.
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