RS-232 Reset for Microprocessor Wiring Diagram Schematic
Introduction
This ambit allows a alien chip to be displace by a authoritative host by sending a breach arresting over an RS-232 or RS-422 consecutive line. If the alien apparatus resets into a simple affairs loader program, it is accessible for the host to arrest and restart, or arrest and reload/restart the alien machine’s program. This is an ideal way to advance software on earlier EPROM-based systems. Modern EEPROM/NVRAM systems use JTAG interfaces for agnate results.
The alien processor runs its ambition cipher out of RAM, acceptance the cipher to be adapted easily. The ambit is usually acclimated for developing cipher on a ambition processor, but it can additionally be acclimated for abiding applications area the ambition affairs lives on a host system’s disk. This arrangement was already acclimated to amount cipher into a microprocessor-based accessory accepting arrangement in Hawaii from a host arrangement in Colorado application an Internet-based alien consecutive communications program.
A affairs loader for the Z80 CPU is accessible below. The ambit has additionally been acclimated with the Motorola 68HC11 EVB and the BUFFALO adviser program. See my Linux Cross Assemblers folio for added info.
Theory
This ambit detects continued continuance aught akin signals (breaks) on a NRZ (non acknowledgment to zero) consecutive abstracts line. Normal consecutive characters absorb a abbreviate time in the aught state, and do not account a reset. Breach signals are a barring to this, they authority the band low for an continued period.
The 10K/1N4148 genitalia accumulate the 2.2uF capacitor answerable up. Low ascribe signals go through the 10K resistor and boring cull the allegation on the 2.2uF capacitor down. High ascribe signals bound recharge the capacitor through the 1N4148 diode. A breach arresting lasts continued abundant to acquittal the 2.2uF capacitor to the point area the afterward aboideau changes state.
The 1N4148 on the appropriate allows a chiral breach about-face to be acclimated on the ambition CPU, acute such a about-face does not abbreviate out the above-mentioned 74HC14 gate.
This ambit could be congenital with aloof 2 schmidt activate non inverting buffers, the 74HC14 was called because it is a accepted part. The alongside inverters are additionally optional, distinct inverters assignment fine.
Z80 Affairs Loader
Here is a Z80 accumulation accent affairs that functions as a bootstrap loader for use with the Chip RS-232 Displace circuit. This cipher runs on an age-old SD systems SBC200 Z80 ambit lath and can be fabricated to assignment with added Z80 boards by alteration the initialization and consecutive anchorage functions.