The new paged-memory card "Schakelkaart"
The card is a double sided PCB with printed legend.
The card adds ten 4K sockets to the Atom.
Eight 4K sockets in memory-space #A000 - #AFFF
Two 4K sockets in memory-space #E000 - #EFFF
(FDC user's are advised to convert that from #Exxx to#1000 - #1FFF), to allow the DOS ROM to reside at #Exxx.
These sockets are numbered A0 to A7 and E0 to E1.
Each of the sockets A0, A1, E0 and E1 could also accept a pair of 2K CMOS memory chips, piggybacked together for 4K.
For the CMOS RAM, the card provides battery backup and a Write Protect circuit.
The card requires that the addresses #Axxx and #Exxx are ‘outside the bus’ only so the card could be connected to that bus and can be used as well inside as outside the Atom.
All data and address lines are buffered on the card. The databus is clocked. For switching-purposes and controlling so the card the address #BFFF has to be put
also 'outside the bus'.
The layout
The address decoder
 Paging-card address coding |
The address decoding by IC7 has caused some problems, due to its unusual way of addressing.
The more flexible coding is shown on this page. Together with the given layout a correct choice can be made for the RAM blocks #Exxx (or #1000) and #A000.
Even the piggyback board to convert the #Exxx to #1xxx on the decoder IC is not needed anymore with the new card. See also the diagram. |
Components
Integrated Circuits
| Ident | Value | Qty | Description | Socket pins | Qty |
| IC9 | 74LS10 | 1 | Triple 3-input NAND gate | 14 | 3 |
| IC4 | 74LS14 | 1 | Hex Schmitt inverter |
| IC10 | 74LS32 | 1 | Quad 2-input OR gate |
| IC8 | 74LS133 | 1 | 13-bit AND gate | 16 | 5 |
| IC5 | 74LS138 | 1 | 8-way decoder |
| IC11 | 74LS47 | 1 | 7-segment display driver |
| IC12-13 | CD4556B | 2 | Dual Binary to 1-of-4 Decoder/Demultiplexer |
| IC1-3 | 74LS244 | 3 | 2 x 4-bit buffer | 20 | 5 |
| IC2 | 74LS245 | 1 | 8-bit buffer |
| IC6 | 74LS273 | 1 | 8-bit register with clear |
| IC14-19 | 2532 | 8 | 4K EPROM | 24 | 11 |
| IC20-27 | 6116 or 2016 | 2 | 2K SRAM |
| IC7 | 74LS154 | 1 | Address decoder |
Note the display driver has open-collector outputs, so it can only drive common anode displays.
Discretes
| Ident | Value | Qty | Description |
| TR1 | BC547B | 1 | Transistor |
| D1 | OA95 | 1 | Small signal diode |
| D2 | Red LED | 1 | |
| D3 | 1N4001 | 1 | |
| R1-23,25,31-32 | 33K | 26 | |
| R24 | 680R | 1 | |
| R26 | 470 | 1 | |
| R27 | 56R | 1 | |
| R28 | 220R | 1 | |
| R30 | 15k | 1 | |
| C1 | 33 µF | 1 | Tantalum |
| C2-4,10 | 15 µF | 3 | Tantalum |
| C5-9,11 | 100 nF | 5 | Ceramic |
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The Display
The card has a spare 16-pin socket where a 74LS47 can be placed to drive a 7 segment display, to show which socket is selected.
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