RS232 Reset for MicroprocessorThis circuit allows a remote microprocessor to reset the control of a host by sending an interrupt signal on an RS-232 or RS-422 serial line. If the remote machine is restarted on a simple program loader program, it is possible that the host to stop and restart, or stop and reload / restart the program the remote machine. This is an ideal way to develop software in EPROM higher based systems. Modern EEPROM / NVRAM systems use JTAG interfaces to achieve similar results.
The remote processor will run your code outside RAM target, which allows code to be updated easily. The circuit is generally used to develop code on a target processor, but can also be used for permanent applications in the target program on the hard lives of a host system. This system was used once to load the code into a microprocessor-based satellite receiving system in Hawaii to a host in Colorado with an Internet-based distance learning program for serial communications.
A program loader for the Z80 CPU is available below. The circuit has also been used Motorola 68HC11 EVB with the monitoring program and Buffalo. See my Linux Cross Assemblers page for more information.
Theory
This circuit detects signals from zero-length (breaks) in an NRZ (non return to zero) of the serial data line. Normal standard characters spend a short time in the zero state, and do not cause a reset. Break signals are an exception to this, hold the line low for an extended period.
The parties maintain 10K/1N4148 2.2uF capacitor charged. Low input signals go through the 10K resistor and slowly pull the load on the 2.2uF capacitor below. The high input signals rapid recharging of the capacitor through the diode 1N4148. A break signal lasts long enough to download the 2.2uF capacitor to the point where the next door changes state.
The 1N4148 on the right allows a manual cutoff switch for use in the target CPU, pressing a switch does not cut the previous 74HC14 gate.
This circuit can be constructed with only two buffers Schmidt trigger investment not, 74HC14 was chosen because it is a common part. Investors are also optional parallel, investors will only work well.
Z80 loader program
This is a Z80 assembly language program that works as a boot loader for use with microprocessor reset circuit RS-232. This code runs on an old SD SBC200 board systems and circuit Z80 can do to work with other boards Z80 changing the initialization and functions of the serial port.
The remote processor will run your code outside RAM target, which allows code to be updated easily. The circuit is generally used to develop code on a target processor, but can also be used for permanent applications in the target program on the hard lives of a host system. This system was used once to load the code into a microprocessor-based satellite receiving system in Hawaii to a host in Colorado with an Internet-based distance learning program for serial communications.
A program loader for the Z80 CPU is available below. The circuit has also been used Motorola 68HC11 EVB with the monitoring program and Buffalo. See my Linux Cross Assemblers page for more information.
Theory
This circuit detects signals from zero-length (breaks) in an NRZ (non return to zero) of the serial data line. Normal standard characters spend a short time in the zero state, and do not cause a reset. Break signals are an exception to this, hold the line low for an extended period.
The parties maintain 10K/1N4148 2.2uF capacitor charged. Low input signals go through the 10K resistor and slowly pull the load on the 2.2uF capacitor below. The high input signals rapid recharging of the capacitor through the diode 1N4148. A break signal lasts long enough to download the 2.2uF capacitor to the point where the next door changes state.
The 1N4148 on the right allows a manual cutoff switch for use in the target CPU, pressing a switch does not cut the previous 74HC14 gate.
This circuit can be constructed with only two buffers Schmidt trigger investment not, 74HC14 was chosen because it is a common part. Investors are also optional parallel, investors will only work well.
Z80 loader program
This is a Z80 assembly language program that works as a boot loader for use with microprocessor reset circuit RS-232. This code runs on an old SD SBC200 board systems and circuit Z80 can do to work with other boards Z80 changing the initialization and functions of the serial port.
