An Input/OUTPUT Port for the Cartridge Slot of the 520ST
By Douglas P. B. Renaux - Feb 27, 1986
This document describes the hardware and software of a 8 lines input/16 lines output port. The circuitry is connected to the Cartridge Slot of the ATARI 520 ST.
IMPORTANT!!! - INFORMATION IN THIS DOCUMENT CAN BE FREELY USED AND COPIED. HOWEVER, NO CHANGES CAN BE MADE TO IT WITHOUT CONSULTING THE AUTHOR FIRST, NOR THE AUTHOR'S NAME CAN BE OMITTED IN THE COPIES.
Foreword
Although the Cartridge Slot is intended for data input, specifically from a ROM, it can be used as an output port. To substitute the READ/WRITE line, that is not available on the slot, I used a WRITE ENABLE LATCH. This latch is set by READING a memory location. The consequence of setting this latch is that the output latches will read the data bus during the next instruction, which will be a memory WRITE that outputs the desired data.
1 - The signals available on the Cartridge Slot
- D0..D15 - DATA BUS
- A1..A15 - The 15 least significant addresses from the ADDRESS BUS ROM 3 SELECT - Active when a READ instruction accesses $FB0000 to $FBFFFF UDS',LDS' - Upper and Lower Data Strobe
2 - The I/O PORT The block diagram of the I/O PORT is in the file BLOCKDIA.PI3. Circuit diagrams are in ADDRESS.PI3 and IN'OUT.PI3. If you don't have these drawings then in appendix A you can read a description of the circuit. The circuit of the I/O PORT is standard. A address decoder enables the out put latches or the input buffers when the correct address is accessed. However, the output latches are only enabled if previously the WRITE ENABLE LATCH was set.
Address Decoder: The lines A3..A15 are connected to NAND gates that detect when all these lines are at high level. The lines A2 and A1, select one of the four outputs of a decoder. The output of the NOR gate "a" is active when we read from $FBFFFE. To decode a read to this address we use the outputs of the two NAND gates, the output three of the decoder (active when A1 and A2 are high) and the line ROM 3 SELECT. The output of NOR gate "a" sets the WRITE ENABLE LATCH.
The output of NOR gate "b" decodes the address $XXFFFC. To decode an access to these addresses (read or write), we use the outputs of the NANDgates, output two of the decoder and the line LDS'. ROM 3 SELECT cannot be used here because it is only active on read. When a write instruction accesses the address $10FFFC (non- existent in 1 MByte ST's) then the output of NOR gate "b" becomes active. An AND gate enables the output latches to read the data bus if theWRITE ENABLE LATCH is set AND the output of NOR gate "b" is active.
The output of NOR gate "b" is delayed (by four inverters) and then resets the WRITE ENABLE LATCH, just after the latches have read the data bus. NOR gate "c" decodes a read to address $FBFFFA, as gate "a" does, but using output one of the decoder. The output of gate "c" enables the buffers to copy their inputs to the data bus.
3 - Components
- 2- 4068 NAND gates for address decoding
- 2- 4002 NOR gates for address decoding
- 1- 4556 1 OF 4 DECODER for address decoding
- 1- 4043 SR FLIP-FLOP write enable latch
- 1- 4049 INVERTER
- 1- 4081 AND2- 40373 LATCHES output latches
- 1- 74LS244 BUFFERS input buffers
4 - Expansion
This I/O PORT is easily expandable to as many I/O lines you want. Only one WRITE ENABLE LATCH is necessary if the expansion is made in a way that any write to port instruction resets the latch. Another solution is to have a reset latch address (as we have a set latch address). In this case the write to port instructions don't need to reset the latch, and you can output a block of data to several addresses without needing to set the latch in between. Only at the end of the block transfer this would be necessary. You can have another 8 inputs by just connecting another 74LS244 to D8..D15 of the data bus.
5 - Software To write to the output lines the contents of D0:
MOVE.W $FBFFFE,D1 ;D1 is destroyed, latch is set
MOVE.W D0,$10FFFC ;D0 is latched To read the input lines to D0:
MOVE.W $FBFFFA,D0 6 - Connection to the ST. I could not find a experiment or PC Board with an edge connector that fits to the ST. So I made a convertor from the 40 pin edge connector (with spacing of 2mm) to a 64 pins euro connector (DIN 41612). This convertor is simply a double sided PCB with 20 lines (on each side) of 1mm spaced by 2mm (center of one line to center of next line). These lines widen to 2.54 mm to fit the DIN connector. Line one of the ST goes to line 4 of the DIN connector.
The tabs of the DIN connector are on the lower side.
______
| | | |. .|
1 |. .| 2 |. .| 3
+ |. .| 4 + Data 15 |. .| 5 Data 14
|. .|
:| | : : | | :
| | Ground |. .| 23 Ground
| | |. .| 31
|. .| 32 | | |
DIN connector seen from front (connection) side
------ I intend to connect some of the free lines of this connector to internal signals of the ST. Would be nice to have a standard connector between ST users. Whoever has ideas about which signals to connect and to which pin should let the others know about it. 7 - Conclusion It is possible to open the ST !!And this opens a lot of possibilities in hardware design. The 68000's power can be used outside the ST's box. But a complex machine like the ST cannot be easily expanded without having information about it. The information that ATARI delivers only to software houses. Please ATARI, let everybody know about the ST.
Let the POWER be available to all users.
Douglas P. B. Renaux
Outshoornstraat 55
5622GX Eindhoven - NL Tel 31-40-436930
(Address valid until May 25, 1986)
People dealing with hardware design are cordially invited to contact me.
APPENDIX A Circuit Description. Block Diagram:
write enable latch ___________ ______|| Read $FBFFFE
| |_____ |
|----------------------|S Q|------------| & |
A15..A1 | ADDRESS | $XXFFFC _________ | |
||---| LDS ----| DECODER |-----T---| Dela
y |----|R| |----||| ROM3 SEL||
|--------- ------ | -----|
|| |__________________________
___|| ||
|
||-----------|
| ----------- Read |
|
$ FBFFFA |
|---------
---------
------------
| || |
| INPUT
| D15 | OUTPUT|
D7..D0-----|BUFFERS|---INPUTS --| LATCHES |--OUT
| | D0
| | | |
| | ---------
------------
Address Decoder Description: Address lines A15 to A3 are connected to the inputs of two 4068(8- input NAND). Inputs are pins 2,3,4,5,9,10,11,12. One of these NAND gates has three inputs tied high. Power supply is connected to pin 14 (+)and pin 7 (ground). The address lines A2 and A1 are connected to the select lines of the4556 (1 of 4 decoder), pins 3 (A2) and 2 (A1). The enable line (pin 1) is tied low. Pins 16(+) and 8 (ground). The outputs of the decoder are: output 0 at pin 4, output 1 (pin 5), output 2 (pin 6), output 3 (pin 7). The second level of the address decoding is done by three NOR gates of four inputs (4002). Two chips are necessary. These gates are labelled"a", "b" and "c".
Pinning of the 4002:
inputs 2,3,4,5; output pin 1 inputs 9,10,11,12; output pin 13 power: pin 14 (+); pin 7 (ground). Two inputs of gate "a" are connected to the outputs of the 4068 (pin13). The third input is connected to ROM3 SELECT and the fourth input goes to output 3 of the decoder. The output of gate "a" is connected to the SET input of the WRITE ENABLE LATCH. Gate "b". Inputs: the two outputs of the 4068s, output 2 of the decoder and LDS. The output of this gate is the line $XXFFFC of the block diagram, it goes to a chain of four inverters (4049) to produce a delay, and it goes to an AND gate. Gate "c".
Inputs: the two outputs of the 4068s, output 1 of the decoder and ROM3 SELECT. The output of gate "c" is inverted by a 4049 and then connected to the enable line of the input buffers (74LS244). Delay chain: The hex inverter 4049 (inputs pins 3,5,7,9,11,14; output spins 2,4,6,10,12,15 respectively) is used. Four inverters are chained to give the desired delay and one inverter is used for the enable of the input buffer. Power is on pin 1 (+) and pin 8 (ground). Note that + is NOT on pin 16! Write enable latch: A 4043 (SR-latch) is used. SET is on pin 4, RESETon 3 and Q on 2. Pin 5 (output enable) is tied low. Power is on pins 16 (+)and 8 (ground). SET is connected to the output of gate "a". RESET goes to the output of the delay chain. AND gate (4081).
Inputs:
Q from the latch (connected to pin 1) and the output of gate "b" (connected to pin 2). The output of this gate (pin 3)enables the output latches. Power is on pins 14 (+) and 7 (ground). Output latches. Two 40373 (octal latches) are used. Inputs (pins 3,4,7,8,13,14,17,18) are connected to the DATA BUS. Outputs (pins 2,5,6,9,12,15,16,19 respectively) are the outputs of the circuit. Pin 1 (output enable)is tied low. Pin 11 (enable latches) goes to the output of the AND gate. Power to pins 20 (+) and 10 (ground). Input buffers. The 74LS244 (inputs 2,4,6,8,11,13,15,17 outputs 18,16,14,12,9,7,5,3 respectively). The inputs of these buffers are the inputs of the circuit. The outputs are connected to the DATA BUS (D0..D7). Pins 1 and19 (output enable) are connected to the inverted output of gate "c". Power to pins 20 (+) and 10 (ground). I used the +5V from the cartridge slot to drive the circuit and 16 leds that monitor the outputs. (The leds are not connected directly to the 40373, but via buffers 4049).
