V2 Changes
Summary of changes
- Updated footprints for large electrolytic capacitors (C1, C2, C3 & C4)
- Replaced 2513 Character Generator with 2764 EPROM
- Implemented Technical Bulletin 63
- Implemented Technical Bulletin 53
- Implemented high-speed cassette interface (3,000 baud)
- Added a RESET push-button switch
- Updated the relay footprint (to suit available 5V/30mA coil relays)
- Updated footprint silkscreen for 20-turn variable resistor (POT1) to better match actual part
- Modify the LED footprint so a 2-pin header can be optionally fitted instead of a LED
- Updated the keyboard keyswitch footprints
- Replaced U4, U5, U10, U12 and U13 (81LS95/97) with 74LS244
- Added a new input pin to the PORT connector (“PORT-9”)
- Disconnected U44/15 from GND (fixed error in V1 layout)
- Added PCB mounting holes
- Enlarged the transformer terminal holes from 0.050″ to 0.070″ (1.78mm)
- Enlarged mounting holes for the RF Modulator
- Changed C17 to 22uF tantalum capacitor
- Changed C14 to 22uF tantalum capacitor
- Changed R33 to 15K
- Enlarged holes for CR1-CR4
- Replaced U18 (74LS174) with octal flip-flop (74LS273)
- Added a new output pin to the PORT connector (“PORT-10”)
- Added ROM-DISABLE circuitry (to allow 64K RAM to be used)
- Rewired ROM sockets for 2732 pinouts (and optionally 2532)
- Added footprint for vertical RCA jack for video output
Changes still to be made:
- Provide option for use of 4164 RAMs
The V2.0 dimensions are 305.0mm by 312.0mm
C1 and C3 (5600uF Capacitors)
C1 and C3 on the original board are 5600uF electrolytic filter capacitors. The voltage rating was not specified, but presumably they should be at least 16V (they filter the input to the 7805 voltage regulators). My original Super 80 is fitted with 5600uF 40V Elna capacitors, which fit the 3 holes in the PCB perfectly. The assembly manual says that C3 is only required if an S-100 card is being used. Taking measurements from the PCB, these capacitors were 1.2″ (30.5mm) in diameter, and the main two pads were 0.6″ (15.24mm) apart. There is also a not-connected third pin which presumably was to physically stabilise the capacitor.
I have not been able to find any suitable capacitors that have 15mm pitch between the pins. Suitable replacement capacitors (5600uF or 10000uF, 16V or 25V) typically have a pitch of 7.5mm or 10mm. So I have modified the footprint for C1 and C3 to accommodate the following:
- Pitch=10mm, Pad=4.7mm, Hole=2.0mm
- Pitch=7.5mm, Pad=3.2mm, Hole=1.2mm
- Pitch=0.6″(15.24mm), Pad=3.2mm, Hole=1.2mm
Suitable currently available replacements for C1 and C3 are (prices exclude GST):
- EPCOS B41231B5109M000 (Digikey P/N 495-6158-ND). 10000uF 25V Snap-in. Diameter=25.4mm, Height=30.0mmm, Lead Spacing=10.0mm. Leads=1.5mm x 0.8mm. Price=AU$2.60/ea
- EPCOS B41231A4109M000 (Digikey P/N 495-6140-ND). 10000uF 16V Snap-in. Diameter=22mm, Height=25mm, Lead Spacing=10.0mm. Leads=1.5mm x 0.8mm. Price=AU$2.08/ea
- Nichicon UHE1C562MHD6 (Digikey P/N 493-1543-ND) 5600uF 16V Radial. Diameter=18mm, Height=31.5mm, Lead Spacing=7.5mm, Lead Diameter=0.8mm. Price=AU$2.47/ea
- Generic 10000uF 25V (Futurlec C10000U25E). Diameter=21mm, Height=41mm, Pin Spacing=10mm, Lead Diameter=Unspecified. Price=US$1.70/ea
C2 and C4 (1000uF Capacitors)
C2 and C4 on the original board are 1000uF electrolytic filter capacitors. The voltage rating was not specified, but presumably they should be at least 25V (they filter the input to the 7812 and 7905 voltage regulators). My original Super 80 is fitted with 1000uF 25V Lihyeh capacitors, which fit the 2 holes in the PCB perfectly. Taking measurements from the PCB, these capacitors were 0.75″ (19.05mm) in diameter, and the main two pads were 0.345″ (8.76mm) apart.
I have not been able to find any suitable capacitors that have 8.76mm pitch between the pins. Suitable replacement capacitors (1000uF or 4700uF, 25V) typically have a pitch of 5.0mm, though a few have a pitch of 7.5mm. So I have modified the footprint for C2 and C4 to accommodate the following:
- Pitch=7.5mm, Pad=3.0mm, Hole=1.2mm
- Pitch=5.0mm, Pad=3.0mm, Hole=1.2mm
Suitable currently available replacements for C2 and C4 are (prices exclude GST):
- Nichicon UVR1E472MHD (Digikey P/N 493-1068-ND) 4700uF 25V Radial. Diameter=16mm, Height=31.5mmm, Lead Spacing=7.5mm. Lead Diameter=0.8mm. Price=AU$2.04/ea
- Nichicon UVR1E102MPD (Digikey P/N 493-1065-ND) 1000uF 25V Radial. Diameter=10mm, Height=20mmm, Lead Spacing=5.0mm. Lead Diameter=0.6mm. Price=AU$0.64/ea
- Generic 1000uF 25V (Futurlec C1000U25E). Diameter=10mm, Height=20mm, Pin Spacing=5mm, Lead Diameter=Unspecified. Price=US$0.35/ea
Replaced 2513 Character Generator with 2764 EPROM
** INSERT A DESCRIPTION OF THE CHANGES **
As part of this change, the clearance between the character generator IC (U27) and the two IC’s to its right (U28 and U30) was increased by 25 mils. This increased clearance will avoid the need to file down the end of the ICs to make them fit into their sockets.
Technical Bulletin 63
On the original S80, the signal /DECODEF (Pin 6 of U50) actually goes low for I/O address ranges F0-FF and E0-EF.
This modification fixes this decoding issue, so that /DECODEF only goes low for address range F0-FF. The modification is fairly simple: The trace from U48/12 to U50/4 is removed, and signal A4 is instead fed into U50/4.
Note that a side effect is that /IORQ is no longer decoded as part of the /DECODEF signal (instead, the I/O device must separately check that /IORQ is low).
Technical Bulletin 53
[insert description]
High-speed cassette interface (3,000 baud)
The PCB now incorporates the MDS Fast Cassette System. This gives the S80 3.000 baud cassette read/write functionality. The existing (low-speed) cassette circuitry has also been retained. Two jumpers (JP4 and JP5) need to be set to the “L” or “H” position, to select the appropriate cassette interface. Note the high-speed cassette uses the same I/O pins as the existing S80 cassette system. This differs from the MDS approach, which used Port 7 for input and Port 5 for output. So some changes will need to be made to the MDS firmware to make the on-board high-speed interface work. The upside of this approach is that the two Port pins continue to be available full-time for other uses.
RESET push-button switch
The standard S80 has two pins available for connection to a RESET switch, but no switch was fitted to the PCB itself. In V2, the two pins are still available, but I’ve also added a small on-board RESET switch in the top-right corner. It is a 6mm tactile push button.
Updated the relay footprint (to suit available 5V/30mA coil relays)
The standard S80 used a modifed 0.3″-wide DIL IC socket footprint for the cassette relay. The S80 energises the coil from +5V via drive transistor Q2. There are relays commonly available that will fit that hole pattern, but the silkscreen perimeter is way off. Another problem is that the 5V relays that suit this hole pattern typically consume 70mA to energise the coil. That’s a lot of energy just to switch the tape deck motor on and off. So I’ve replaced the relay footprint with a 0.2″ spacing pattern. This accommodates 5V relays that typically consume 30mA of coil power, and have an outline of 0.5″ x 0.3″. Samples include the TSC-105L3H from element14, or the JRC-23F-05 from Futurlec.
Updated footprint silkscreen for 20-turn variable resistor (POT1) to better match actual part
The silkscreen pattern (but not the hole placement) has been updated to suit currently available parts, such as Futurlec CERMR20K or Bourns 3006P series trimpots.
Updated LED footprint
Changes have been made to allow a 2-pin header to optionally be fitted instead of the LED. This is so the LED can be mounted external to the PCB. The spacing between the pins had to be adjusted slightly (from 105 mils to 100 mils) and the hole sizes were increased from 24 mils (0.6mm) to 36 mils (0.9mm). The pads were changed from circular 45 mils (1.1mm) to oval-shaped 85 mils (2.1mm) by 75 mils (1.9mm).
Updated keyswitch footprints
The keyswitch footprints have been updated to suit the keyswitches that Ewan should be able to source for us. The 2 pins are arranged vertically on the new keyswitches (the original keyswitches had the pins arranged horizontally). As a result, almost all the traces on the keyboard had to be pulled up and relaid. Another consequence of the keyswitch change is that the bottom edge of the PCB had to be extended by 0.060″ (approx 1.5mm) to accommodate the bottom keyswitch.
Replaced 81LS95/97 with 74LS244
This involved rewiring the footprints for U4, U5, U10, U12 and U13. When replacing U10 I found that the original S80 PCB layout has a circular net on D0. On the original S80 you will see that there are D0 traces leading to the right from both U10/3 and U18/3. These two traces connect up under U12. I removed one of these redundant traces (the upper one) when replacing U10 with a 74LS244.
Connected new PORT-9 input pin to U10/4 (Bit D3 of /INPORT)
On the original S80, only 7 gates of U10 (octal input buffer) were used. Data bit D3 had been left unconnected. When I replaced U10 with a 74LS244 I decided to connect up the unused bit. D3 now reads a new input pin called “PORT-9” on the PORT I/O header.
Disconnected U44/15 from GND
On the V1 reproduction PCB, U44 Pin 15 had been inadvertently connected to GND. This error has been corrected. U44 Pin 15 now floats high instead.
Added PCB mounting holes
Mounting holes (3.0mm diameter) have been added to the PCB. The corner holes are located 6.0mm in from the PCB edges. An additional two holes have been added 6.0mm above the dashed line separating the main PCB from the keyboard PCB. These two additional holes are also 6.0mm from the side edges of the PCB.
Enlarged the transformer terminal holes from 0.050″ to 0.070″ (1.78mm)
This was necessary as the header pins are 1.50mm on the diagonal. I made this change to both the V2 PCB and the library component (S80-J1-TRANSFORMER).
Enlarged mounting holes for the RF Modulator
The existing holes were 0.060″ (approx 1.5mm). Peter advised that the pins are 2.3mm in diameter. So I have enlarged these holes to 0.100″ (2.54mm). The pad size was increased from 0.125″ to 0.150″. I made these changes to both the V2 PCB and the library component (S80-RF-MOD-ORIG).
Changed C17 to 22uF tantalum capacitor
On the V1 PCB I specified C17 as being a 33uF Tantalum. This matches the value shown in the schematic in the Assembly Manual. However the parts list in the Assembly Manual specifies 22uF tantalum and that is what is actually installed in my real Super 80. So I have reduced the value to 22uF on the schematic. No change was required to the PCB.
Changed C14 to 22uF tantalum capacitor
On the V1 PCB I specified C14 as being a 25uF/25V capacitor. This matches the value shown n the schematic in the Assembly Manual. However the parts list in the Assembly Manual specifies 22uF tantalum and that is what is actually installed in my real Super 80. So I have made this change to C14 on the schematic. No change was required to the PCB.
Changed R33 to 15K
R33 (pullup resistor at the base of the video driver transistor) is shown in the EA schematic as being 10K, and that is what is shown in my KiCAD schematic for the V1 PCB. But this was changed to 15K in the schematic and parts list in the Assembly Manual. My original S80 has a 15K resistor fitted here. So I used a 15K resistor during assembly of the V1 Reproduction. The KiCAD schematic for the V2 PCB has been updated to show a 15K resistor.
Enlarged holes for CR1-CR4
These holes were 0.050″ (1.27mm). I have enlarged them to 0.060″ (1.52mm) to accommodate the MUR420G diodes that I am using. I made this change both to the V2 PCB and the library component (S80-D600-50).
Replaced U18 with octal flip-flop (74LS273)
In the original S80, U18 was a 74LS174 hex flip-flop. Bits D6 and D7 were unused. I have replaced U18 with a 74LS273 (octal d flip-flop with clear). D6 now connects to a new “PORT-10” output on the “PORT” connector. D7 now optionally allows the ROMs to be switched out of the memory map (this will be useful for a future CP/M implementation). Pin 1 (/MR) of U18 was originally left floating high. It is now wired to SOD*. So all outputs will be forced LOW on reset, and will continue to be forced low until user code reads an instruction from address C000-FFFF. U10 and U18 were moved 25 mils to the right, to provide adequate clearance between C4 and U18.
Added ROM-DISABLE circuitry
The original S80 has ROM space permanently enabled in the range C000-FFFF. I’ve added circuitry to allow the ROMs to be switched out, so that all 64K can be used for RAM. This will be beneficial for running CP/M on the S80 in the future. This functionality has been implemented by using one of the two new flip-flops of U18 (bit D7). This output (which I’ve labelled ROM-DISABLE) has been wired to U32/4, which was previously hardwired to GND. On reset the ROM-DISABLE bit is LOW (because pin 1 of U18 has now been wired to SOD*). If user code intervenes and sets bit D7 of U18 high, the ROMs will be disabled and RAM will be available from 0000-FFFF. This is obviously hazardous if bit D7 is accidentally set high, so a new 3-pin header has been added to enable or disable this new functionality.
Rewired ROM sockets for 2732 pinouts (and optionally 2532)
On the original S80, the 3 ROM sockets (U26, U33 and U42) were wired by default to suit 2516/2716 EPROMs and by a simple modification 2532 (but not 2732) EPROMs could be used instead. I have modified the circuitry now so that by default the V2 S80 PCB expects 2732 or 2732A EPROMs, and by modifying 4 PCB jumpers 2532 EPROMs can be used instead.
Added footprint for vertical RCA jack for video output
On the original S80, just above the video modulator there are 2 pads for un-modulated composite video output. I have replaced these pads with a footprint to suit a vertical RCA jack. The part is RCJ-024 (or any RCJ-02x part) manufactured by CUI Inc (Digikey part number CP-1409-ND). Note that this RCA jack may interfere with the placement of the video modulator.
Replacing 4116 RAM with 4164
Let's have another look at the pinouts of the 2 RAM types:
___ ___ ___ ___
-5v -|1 \/ 16|- Gnd n/c -|1 \/ 16|- Gnd
Din -|2 15|- /CAS D -|2 15|- /CAS
R/W -|3 4 14|- Dout /WE -|3 4 14|- Q
/RAS -|4 1 13|- A6 /RAS -|4 1 13|- A6
A0 -|5 1 12|- A3 A0 -|5 6 12|- A3
A2 -|6 6 11|- A4 A2 -|6 4 11|- A4
A1 -|7 10|- A5 A1 -|7 10|- A5
+12v -|8 9|- +5v Vcc -|8 9|- A7
-------- --------