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boards:ecb:mf-pic:secondary [2016/03/12 10:11]
will
boards:ecb:mf-pic:secondary [2016/03/12 14:32] (current)
will
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 The interrupts from the UART and IDE device are sent over the ECB bus to the interrupt controller on the primary MF/PIC board, so this board will only operate as a secondary device in a system which already includes a primary (ie fully functional) MF/PIC controller. You may have up to four secondary MF/PIC boards in the system since each board uses two ECB interrupt lines, of which there are eight available in the system. The interrupts from the UART and IDE device are sent over the ECB bus to the interrupt controller on the primary MF/PIC board, so this board will only operate as a secondary device in a system which already includes a primary (ie fully functional) MF/PIC controller. You may have up to four secondary MF/PIC boards in the system since each board uses two ECB interrupt lines, of which there are eight available in the system.
  
-The secondary MF/PIC board described here also replaces the RS232 port with a USB interface using an FTDI FT232RL breakout board (readily available on ebay for around $3). By fitting a 16MHz oscillator baud rates up to 1Mbit/sec may be achieved.+The secondary MF/PIC board described here also replaces the RS232 port with a USB interface using an FTDI FT232RL breakout board (readily available on ebay for around $3; be sure to get one which makes the RTS and CTS pins available). By fitting a 16MHz oscillator baud rates up to 1Mbit/sec may be achieved.
  
 To construct the secondary board, fit **only** the following components: To construct the secondary board, fit **only** the following components:
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   * U8 (74LS244)   * U8 (74LS244)
   * U9 (74LS688)   * U9 (74LS688)
-  * U14 (74LS245) 
   * U10 (74LS02)   * U10 (74LS02)
   * U11 (74LS04)   * U11 (74LS04)
   * U13 (74LS139)   * U13 (74LS139)
 +  * U14 (74LS245)
   * U22 (82C55)   * U22 (82C55)
   * U27 (74LS32)   * U27 (74LS32)
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   * P3, P4 (13×2 and 20×2 IDC headers)   * P3, P4 (13×2 and 20×2 IDC headers)
   * P5 (I/O address selection jumpers)   * P5 (I/O address selection jumpers)
-  * Capacitors (C0 and all decoupling caps+  * Capacitors (C0 and decoupling caps, I chose to fit all the decoupling caps even those for unpopulated ICs although this is probably excessive)
  
-At position J3 I fitted a PPTC 30V 0.9A resettable fuse between the center and +5V pins. This provides good protection against accidentally plugging the IDE device in incorrectly.+At high speeds it is recommended to fit **74LS**  family logic for all bus transceivers as these have superior immunity to bus noise.
  
-Instead of U32/U33 (MAX232/MAX235) I fitted a FT232RL TTL serial to USB adapter breakout boardI used hot-glue to secure the breakout board where the supercapacitor would normally live, on the top left of the boardI set the I/O voltage selection jumper on the FT232RL board to "5V"I then used patch wires to connect the breakout board to the footprint that the MAX232 would normally occupy:+At position J3 I fitted a 30V 0.9A [[https://en.wikipedia.org/wiki/Resettable_fuse|PPTC resettable fuse]] between the center and +5V pinsThis provides good protection against accidentally plugging the IDE device in incorrectly, which may otherwise short out +5V and GND and burn out a PCB trace.
  
-  * FT232RL "GND" pin to J3 pin 1 (GND) +Instead of U32/U33 (MAX232/MAX235I fitted a FT232RL TTL serial to USB adapter breakout board. I used hot-glue to secure the breakout board where the supercapacitor would normally live, on the top left of the board. The hot-glue gives mechanical stability and ensures an insulating layer between the breakout board and the main PCB. I set the I/O voltage selection jumper on the FT232RL board to "5V". I then used patch wires to connect the breakout board to the footprint that the MAX232 would normally occupy:
-  * FT232RL "RTS" pin to U32 pin 9 +
-  * FT232RL "CTS" pin to U32 pin 10 +
-  * FT232RL "RXD" pin to U32 pin 11 +
-  * T232RL "TXDpin to U32 pin 12+
  
-The interrupt lines from the IDE interface and the UART interfaces are the wrong polarity (active highso it is necessary to route them through spare inverters on the board before connecting them to the ECB interrupt lines (which are active low). All the ECB interrupt lines are easily accessible on the footprint for the unfitted RP1 resistor network, so you can easily choose which ECB IRQ lines each device connects to.+  * FT232RL "**GND**" pin to J3 pin 1 (**GND**) 
 +  * FT232RL "**RTS**" pin to U32 pin 9 
 +  * FT232RL "**CTS**" pin to U32 pin 10 
 +  * FT232RL "**RXD**" pin to U32 pin 11 
 +  * FT232RL "**TXD**" pin to U32 pin 12 
 + 
 +The interrupt lines from the IDE interface and the UART interfaces are active high but the ECB IRQ lines are active low, so it is necessary to route them through spare inverters on the board. All the ECB interrupt lines are easily accessible on the footprint for the unfitted RP1 resistor network, so you can easily route each device's interrupt to any ECB IRQ line.
  
 To route the IDE interrupt: To route the IDE interrupt:
  
   * Connect U10 pin 8 to U10 pin 9   * Connect U10 pin 8 to U10 pin 9
-  * Connect U10 pin 9 to U15 pin 8 (note: chip not fitted, this is just a convenient GND) via a 10K resistor; this pulls the interrupt line low when no card is inserted.+  * Connect U10 pin 9 to U15 pin 8 (note: chip not fitted, this is just a convenient GND) via a 10K resistor; this pulls the interrupt line low when no disk is connected.
   * Connect U10 pin 8 to P4 pin 31   * Connect U10 pin 8 to P4 pin 31
   * Connect U10 pin 10 to RP1 pin 2 (ECB IRQ 7)   * Connect U10 pin 10 to RP1 pin 2 (ECB IRQ 7)
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 </code> </code>
  
-Happy hacking!+Photos of my completed board are included below for reference. 
 + 
 +{{:boards:ecb:mf-pic:mfpic-secondary-front-scaled.png?nolink&1024x1788}}{{:boards:ecb:mf-pic:mfpic-secondary-back-scaled.png?nolink&1024x1728}}
  
boards/ecb/mf-pic/secondary.1457795516.txt.gz · Last modified: 2016/03/12 10:11 by will
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