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---
title: Connectors on the Wavedrum's circuit board
tags: DIY,electronics,music,hacking,wavedrum
---
On the circuit board of the Wavedrum there are solder holes to
accomodate three large connectors. Since they are so easily
accessible and thus very inviting to anyone interested in modifying
the instrument, I decided to trace each of the pins to its
destination.
The three connectors are named CN10, CN11, and CN12, respectively.
CN10 is found on the bottom right, CN11 on the bottom left, and CN12
close to the left edge below the micro SD card reader.
<img class="full stretch" src="/images/posts/2013/wavedrum-connectors.jpg" alt="connectors on the mainboard" />
# CN10: digital audio interface
Most of the ten pins of CN10 are outputs. The first three pins carry
clock signals used by the analogue to digital and digital to analogue
converters on the top-side of the board. Pin four gives access to the
PDN (power down) signal which is used to disable the converters. The
next three pins are connected over the resistors R85, R84, and R83 to
the DSP's pins 145, 144, and 143 (respectively); according to the
[DSP's datasheet](http://www.analog.com/static/imported-files/data_sheets/ADSP-21371_21375.pdf)
these pins are `DAI_P8` (`SFSI`), `DAI_P10` (`SD2B`), and `DAI_P11`
(`SD3A`), and are thus part of the Digital Audio Interface (DAI). The
remaining three pins on CN10 expose the supply voltage, ground, and an
alternative positive voltage (the same as on the plus pole of the
silver capacitors near the right edge of the board). These are the
signals left to right:
. | direction | description
---|-----------|-----------------
1 | output | Master clock
2 | output | Audio serial clock
3 | output | Left/right clock
4 | output | `PDN` (power down)
5 | input? | `DAI_P8` / `SFSI`
6 | input? | `DAI_P10` / `SD2B`
7 | input? | `DAI_P11` / `SD3A`
8 | output | V_A, or V_DD
9 | output | GND
10 | output | alternative positive voltage
What is this all good for? Well, since all these clocks and voltages
are exported it becomes relatively easy to connect an external digital
to analogue converter (when `DAI_P8`, `DAI_P10`, and `DAI_P11` are
used as outputs), or an external analogue to digital converter (if the
DSP pins are used as inputs instead). As there are protective
resistors between the DSP pins and the connector pins 5--7 I assume
that they are supposed to be used as inputs.
# CN11: JTAG interface
Moving on to the left bottom edge of the board we see a 14-pin
connector with the name CN11. This connector gives access to the JTAG
interface on the DSP, which allows system debugging. Unfortunately, I
don't own a JTAG dongle and the free JTAG debugger
[OpenOCD](http://openocd.sourceforge.net) does not support the SHARC
core, so I haven't been able to experiment with the debugging
interface. I'm not sure whether it is possible to use debugging
feature without hardware/software provided by Analog Devices. Using
JTAG it should be possible to overwrite the flash memory and replace
the firmware. This is the most promising method to upgrade (or
downgrade) a Wavedrum.
The pins on the bottom row are all connected to ground, so the
following table only lists the signal names of the upper row of the
connector in order from left to right:
. | Signal | Full name
--+---------+------------------------
1 | `~EMU` | Emulation status
2 | `GND` | Ground
3 | `TMS` | Test mode select
4 | `TCK` | Test clock
5 | `~TRST` | Test reset
6 | `TDI` | Test data input
7 | `TDO` | Test data output
# CN12: two-wire serial interface
CN12 exposes the DSP's two-wire interface, a serial interface
compatible with the proprietary I^2C interface. This allows us to
connect a number of external serial devices to the serial bus. As
firmware support is required to communicate with the devices on the
serial bus I don't see how this could be used without a custom
firmware.
The following table lists the signals from top to bottom:
. | Signal | Full name
--+------------+------------------------
1 | `V_D` | Positive voltage
2 | `TWI_DATA` | Two-wire interface data
3 | `TWI_CLK` | Two-wire interface clock
4 | `GND` | Ground
# Bonus: boot mode
What led me to tracing the routes of the connectors was my curiosity
about the boot mode. According to the DSP's datasheet, there are four
possible boot modes to select from by playing with the states of the
pins `BOOT_CFG1-0` (one of these boot modes is "no boot"). Tracing
these two pins from the DSP it becomes clear that the third boot mode
"EPROM/FLASH boot" is hardwired (`BOOT_CFG1-0 = 10`). The other two
usable boot modes are SPI master and slave boots.
BOOT_CFG1-0 | Booting Mode
-------------+--------------------
00 | SPI Slave Boot
01 | SPI Master Boot
10 | EPROM/Flash Boot
11 | No boot
<img class="full stretch" src="/images/posts/2013/wavedrum-bootcfg.jpg" alt="boot configuration traces" />
As can be seen on the photo, the Wavedrum engineers were kind enough
to leave solder pads connected to boot configuration pins on the
board, allowing us to rewire them as we see fit. To set `BOOT_CFG0`
the pads for `R72` have to be bridged; likewise, to clear `BOOT_CFG1`
only the two pads of `R59` have to be bridged.
# References
- [ADSP-21371/ADSP-21375 datasheet](http://www.analog.com/static/imported-files/data_sheets/ADSP-21371_21375.pdf)
- [ADSP hardware reference](http://www.analog.com/static/imported-files/processor_manuals/ADSP-21367_hwr_rev2-1.pdf)
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