Lee Hart has produced a varient of the COSMAC ELF, an RCA 1802 CPU based micro, called "the 1802 Membership Card. This note discusses standby current consumption of the 1802 processor as manipulated by various input status lines. Current production of the 1802 Membership Card, is described and priced on the "membership card" home page. That home page also has links to software and hardware, notes and documents, and more resources.
Last updated May 13 2017. Edited by Herb Johnson. from posting in cosmacelf May 2017 by Lee Hart and Herb Johnson.
Reported May 2017: "My 1802 MC (Rev H) has one odd behavior. When in "standby" (V+ connected to 4.5v and RUN and LED open) it draws about 1.8 mA which seems way high. Front panel switch positions don't seem to have an effect on this. System is 32K SRAM / 32K EEPROM, configured for inverted RS-232 logic and general purpose I/O. Current when running is 6-8 mA depending on front panel activity. The clock does stop when the RUN line is opened."
Herb Johnson replied:
When the 4-pin power cable is removed, power from the supercap is disconnected from the front- panel logic. The front-panel logic becomes passive, unpowered. I don't know how much power it draws as a result, but not likely much.
You are apparently saying, with both CPU and front-panel card together, "standby" power draw is 1.4mA.. If any memory is enabled, it will "drive" bits on the data bus. The active memory driver logic in RAM chips, often draws current. Memory select logic, may draw various amount of current. Some RAM chips, like EEPROM, may draw more current than others when in low-power mode - check their data sheets for details. At your own risk, you can test by measuring current in the M/S card with chips removed or in place.
One milliamp is not much - one amp-hour of current capacity would last over a MONTH. A milliamp at 5 volts is drawn by a 5K resistor. If any LED is on, that's a milliamp or more right there. Obviously, you can turn on or off an LED to determine current draw.
There are changes from one rev to another on the CPU boards - particularly the memory-address circuits. Have you looked at the Rev H Web page, or earlier-rev Web pages, for notes about changes. A list of various revision Web pages is maintained on the "home" page. - Herb Johnson, May 2017
The Front Panel board's serial interface has some resistors that will draw current if the logic levels are in the wrong state. Look at the circuit, how you have the jumpers configured, and what your external serial signals are doing.
Also, note that modern high-speed RAMs and EPROMs take significantly more standby power than the older slower ones. - Lee Hart, May 2017
The 1802 enters an odd state before the first LOAD after CLEAR. As a result the 1802 circuits can draw more current than expected. Read this Tech Note for details.
This page and edited content is copyright Herb Johnson (c) 2017. Copyright of other contents beyond brief quotes, is held by those authors. Contact Herb at www.retrotechnology.com, an email address is available on that page..