The No-Slot Clock project was started about mid 2014 by Henry from ReActiveMicro, and was officially released on April 12th, 2015. It was inspired by his work on the DClock project. The No-Slot Clock project will fit in the Apple //c, //c plus, however it can be a very tight fit with a //c 1Meg RAM Card installed.
Theory of Operation: The /CE (Chip Enable) signal from the systems' DIP Socket passes through the DS1215 Clock IC (in Pin11, out pin10). When the DS1215 Clock IC recognizes a certain sequence of bits on A0 (Pin6) and A2 (Pin3) the ROM's /CE pin is held high by the DS1215 Clock IC and is in essence "disconnected" from the systems' data bus. This allows the No-Slot Clock's software to communicate directly with the DS1215 Clock IC without the ROM interfering.
Project Status: UM collaboration discontinued in 2016. RM version currently under development.
While working on the DClock project Henry learned how phantom clocks work. With this understanding he was able to see how a new and better No-Slot Clock design could be produced.
When Henry started the No-Slot Clock project he purchased back stock of the DS1215 Clock ICs from James Littlejohn of 8bitsystem.com on June 13th, 2014. James had abandoned the DClock project and wasn't using the stock Henry had previously sold to him.
Henry then started CAD and design work for his version of the No-Slot Clock to come up with a better design that didn't use two DIP Sockets soldered together, as Dallas did with their "SmartWatch" Clock design. The reason for this is not all signals are passed from the systems data bus to the ROM or RAM IC the DS1216E No-Slot Clock is installed under.
The initial v1.0 project was an Ultimate-Micro collaboration. All Ultimate-Micro releases bare the UM logo, and the last revision was v1.3 which was discontinued in 2016 when ReActiveMicro returned from hiatus.
Henry restarted Active development of the project in 2019.
All previous UM versions are very similar. They all use SMT pads for the CR1025 Battery Holder, the Crystal, and DS1215 Clock IC. They all also offer two SMT pads for connection of an auxiliary power source. This could be supplied by soldering two .025 mil Square Pins to the SMT pads and using the IIgs_ROM0/1_Battery_Caddy or similar 2x AA/AAA Battery Caddy.
The footprint for the Crystal is designed in such a way to allow for several body styles. 1206, 4-SMD, and Surface Mount Cylindrical Can styles can all be used.
A CR1025 Battery Holder isn't available for the custom footprint on the PCB. As a result, when a unit is assembled the Battery Holder is modified to fit the board.
There is also a custom footprint used for the SIP Header Pins. They are used as the Socket for the ROM, and pass-through the PCB to make contact to the systems' DIP Socket on the motherboard. You will notice in the pics of the PCB that one via pad is NOT drilled out. This is to isolate the /CE signal as mentioned above. During assembly Henry uses a drill to make a hole on the top side that doesn't fully pass through the board. He then clips the leg from the SIP Header pin which allows the rest of the pins to fully seat flush to the PCB while maintaining the isolation of the /CE signal. He then solders the clipped pin leg to the bottom of the board.
- v1.0 was produced about November 2014. While working with this design Henry noticed that some of the DS1215 Clock IC had issues. Some were slow. Some were fast. Some didn't advance the time at all. Henry assumed this was due to the Crystal and changed stock a few times in an attempt to resolve the issue. Henry also noticed the CR1025 Battery Holder could easily be broken off the PCB. Only a few v1.0 units were produced and mostly sent to beta testers.
- v1.1 was produced about January 2015. This design allowed for a more sturdy PCB mounting of the CR1025 Battery Holder. The SMT pads now covered a lot larger area and were not as easily ripped off the PCB. This design however still suffered from the same issues with keeping time as with v1.0.
- v1.2 was produced around April of 2015, however the design had an error. The solid pad for the /CE signal was drilled out. So this design could not work.
- v1.3 was produced around August of 2015, however the design also had the same error as v1.2. The CAD software used was EZ-PC CAD and it is somewhat hard to control pads and layers. Henry then switched to KiCAD and fully relaid out the design. This version is the first to sport the new "UM" logo. It also was an attempt to resolve the time keeping issue. Henry found that the length of the connection between the DS1215 Clock IC and Crystal mattered, even as short as they were on the design. There most likely was a resonance issue. Henry also added a ground plane shield under the Crystal.
- The next v1.3 version was produced around March of 2016. Henry now used KiCAD and had much better control of the design, which really shows in this version. The via for the /CE signal is now correct and not drilled out. The grounding plane shield now extends the full Crystal area and now runs under the DS1215 Clock IC. The connections between the DS1215 Clock IC and Crystal are now of the same length and also shielded with the ground plane. There is also the new, now legible "UM" logo as well as larger name and version information. Lastly, this design now features the "notch" area and marking to allow the user to more easily identify Pin1 of the design when installing the No-Slot Clock.
v1.3 was the last stable release version from UM. All issues mentioned above have been resolved. And the project was discontinued in mid-2016 when ReActiveMicro returned from hiatus.
The ReActiveMicro No-Slot Clock v1.0 proto. Development started in late 2019 once Henry was able to source Lead Frame pins. The pin allow 'legs' to be mounted to the edge of a PCB, which creates a DIP module. The legs are identical to DIP ICs, so there's no longer any socket stretch. And the new design also allows for the project to be factory assembled to help reduce costs and allow for better stock and quality control unlike the previous versions.
Known Design Issues
There currently one known issue with the current design.
Using SIP Header Pins in old, inferior quality Sockets on the motherboard can cause "Socket Stretch". This is where the spring contacts in the motherboard Socket are deformed when the thicker SIP Header Pin is inserted.
The issue only becomes apparent when the original ROM is reinserted into the motherboard Socket and doesn't make good contact. Symptoms mainly show as a system not booting and acting like the ROM isn't inserted in the motherboard Socket. Sometimes pressing firmly on the ROM will cause it to make temporary contact with the stretched Socket and the computer will start to work, only to fail again when pressure is removed from the ROM or the motherboard lightly tapped.
The only solution is to replace the damaged Socket with a new, high quality one.
A majority of Apple II systems seem to have issues with Socket Stretch, which is why ReActiveMicro products have started to make the move to use DIP Plugs in place of Header Pins. Some Apple II systems don't exhibit Socket Stretch, however there is no known way to tell what systems won't be affected or were manufactured with lower quality Sockets. They all visually appear the same.
The No Slot Clock design is well tested in the Apple II. So far the only known issue exists with the Microsoft Z-80 SoftCard. No damage will occur, however the Apple II will tend to lock up on boot.
There have been reports that sometimes the Apple II will work correctly with the SoftCard in Slot 5.