Semiconductor manufacturers have designed several
types of circuit supervisors with varying types of func-
tionality over the past few years. Some supervisors
incorporate watchdog features as well as complex func-
tions, such as programmable threshold levels. As it
turns out, most system supervisor data sheets address
typical supervisor functions related to Power-on Reset,
power-down, and brown-out conditions. In order to
serve a wide customer base, semiconductor manufac-
turers should also address system supervisors
designed into systems where microcontrollers (MCUs)
and programmable logic devices (PLDs) are pro-
grammed in-circuit. Programming PICmicro
®
micro-
controllers in this fashion is known as In-Circuit Serial
Programming
TM
(ICSP
TM
), which can be implemented
for a variety of reasons, including field upgrades.M AN820
System Supervisors in ICSPTM Architectures
Author: Ken Dietz
CIRCUITRY BACKGROUND
Microchip Technology Inc.
MCP120 Output Stage
A simplified schematic for the MCP120 output stage is
shown in Figure 1. Nominally, the output stage of the
MCP120 can handle sinking less than 1 mA of current
INTRODUCTION in a high impedance stat……
