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Four analog comparators are provided on chip which can provide a great effect on NXP MCU P87C554 Embedded Firmware Unlocking. Three comparators have a common negative reference CMPR- and independent positive inputs CMP1+, CMP2+, CMP3+ on port 3.

The fourth comparator has independent positive and negative inputs CMP0+ and CMP0- on port 1. The CMP register contains an output and enable bit for each comparator. The CMP register is bit addressable and is located at SFR address E8H. below Figure shows the connection of the comparators.

analog comparator

Pullups at the comparator input pins will be disabled by hardware when the comparator is enabled. In addition, to make inputs high impedance with similar procedure of Get Microcontroller P89C536 Embedded Firmware, the corresponding port SFR bits must be set by software to disable the pulldowns. Upon reset SADDR (SFR address 0A9H) and SADEN (SFR address 0B9H) are loaded with 0s. This produces a given address of all “don’t cares” as well as a Broadcast address of all “don’t cares”.

NXP MCU P87C554 Embedded Firmware Unlocking

This effectively disables the Automatic Addressing mode and allows the microcontroller to use standard 80C51 type UART drivers which do not make use of this feature. The Broadcast Address for each slave is created by taking the logical OR of SADDR and SADEN. Zeros in this result are treated as don’t-cares. In most cases, interpreting the don’t-cares as ones, the broadcast address will be FF hexadecimal which can manipulated in the process of Microcontroller copying.