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annotate DUART-cable @ 28:3799892b1a79

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Quadband-ideas article rewritten for the new situation since Tango discovery
author Mychaela Falconia <falcon@freecalypso.org>
date Sat, 25 Jan 2020 22:41:11 +0000
parents f7ed8c45a8ec
children 78c2cc6ebbb8
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27
f7ed8c45a8ec DUART-cable article written
Mychaela Falconia <falcon@freecalypso.org>
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1 The Calypso chip has two UARTs, called MODEM and IrDA in the chip docs. The
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Mychaela Falconia <falcon@freecalypso.org>
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2 primary UART (MODEM) has 4 signals (TxD, RxD, RTS and CTS), whereas the other
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Mychaela Falconia <falcon@freecalypso.org>
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3 UART (IrDA) has data leads only (TxD and RxD). TI's C-Sample and D-Sample
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4 boards have also established a convention whereby Calypso GPIOs 2 and 3 have
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Mychaela Falconia <falcon@freecalypso.org>
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5 been assigned as supplementary modem control signals for the primary MODEM UART,
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6 with GPIO 2 being an output from Calypso signaling DCD to the host and with
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7 GPIO 3 being an input to Calypso receiving DTR from the host. Note that DSR
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Mychaela Falconia <falcon@freecalypso.org>
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8 and RI are still missing in this arrangement.
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9
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10 In FreeCalypso we have further established our own convention: all FC hardware
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11 products that bring out both Calypso UARTs do so by way of a single 10-pin (2x5)
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12 2.54 mm header in a fixed pinout given below. This convention was started with
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13 FCDEV3B, our first FC hw product, and is now being continued with MMTB1 and
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14 other boards. Our standardized DUART header pinout is as follows:
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15
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16 Header pin Calypso signal
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17 1 GND
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18 2 GND
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Mychaela Falconia <falcon@freecalypso.org>
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19 3 TX_IRDA
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20 4 TX_MODEM
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21 5 RX_IRDA
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22 6 RX_MODEM
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23 7 GPIO2_DCD
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24 8 RTS_MODEM
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25 9 GPIO3_DTR
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26 10 CTS_MODEM
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27
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28 Pins 7 and 9 were originally left unused (they are unconnected on FCDEV3B), but
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29 they have been assigned as DCD and DTR (from the host's perspective) starting
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Mychaela Falconia <falcon@freecalypso.org>
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30 with MMTB1. Note that while DCD and DTR in the table above are named from the
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31 host's perspective, all Calypso signals ending with _MODEM or _IRDA are from
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32 the chip's perspective, i.e., the opposite.
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33
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34 Our standard recommended practice for connecting to our two UARTs from a regular
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Mychaela Falconia <falcon@freecalypso.org>
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35 PC or laptop is to use FT2232D breakout boards from the following vendor:
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36
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37 http://pldkit.com/other/ft2232d-module
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38
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39 FT2232D is a versatile USB-to-various-things adapter, but in its default
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40 configuration which we use here it acts as a bridge from USB to two UARTs,
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41 presenting both UARTs behind a single USB device. The breakout board made and
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42 sold by PLDkit has two rows of header pins, featuring 15 pins on each side, and
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43 the two sides of the board neatly correspond to the A and B sides of FT2232D.
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44
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45 Our standard recommended method for connecting our two UARTs to a PLDkit FT2232D
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46 board is to use a 10-wire ribbon cable that is custom-assembled as follows:
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47
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48 * One end is terminated with a 10-pin female connector that mates with the DUART
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49 header on our modem boards;
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50
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51 * The other end is split into two parts as described below, and each split end
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52 is terminated with a 15-pin female connector that mates with one side of the
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53 FT2232D breakout board.
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54
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55 The split between A and B sides on the FT2232D end is not symmetric, instead 7
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56 wires go to side A for the MODEM UART and 3 wires go to side B for the IrDA
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57 UART. Assuming the standard color code, the 10-wire ribbon cable gets split
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58 between violet and grey wires: brown to violet go to side A, grey to black go
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59 to side B. After each wire has been stripped and fitted with a crimp-on female
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60 terminal, FT2232D side A wires need to be inserted into the connector housing
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61 as follows:
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62
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63 Wire Pin position FT2232D signal UART signal (host perspective)
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64 brown 2 ADBUS0 TxD
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65 red 3 ADBUS1 RxD
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66 orange 4 ADBUS2 RTS
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67 yellow 5 ADBUS3 CTS
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68 green 6 ADBUS4 DTR
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69 blue 8 ADBUS6 DCD
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70 violet 15 GND GND
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71
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72 FT2232D side B wires need to be inserted into the other connector housing as
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73 follows:
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74
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75 Wire Pin position FT2232D signal UART signal (host perspective)
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76 grey 2 BDBUS0 TxD
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77 white 3 BDBUS1 RxD
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78 black 15 GND GND
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79
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80 The wires on the other end of the cable (also stripped and fitted with crimp-on
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81 female terminals) need to be inserted into another connector housing that will
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82 mate with the DUART connector on FreeCalypso modem boards; the pin assignment
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83 is as follows:
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84
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85 Pin position Calypso signal Wire
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86 1 GND black
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87 2 GND violet
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88 3 TX_IRDA white
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89 4 TX_MODEM red
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90 5 RX_IRDA grey
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91 6 RX_MODEM brown
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92 7 GPIO2_DCD blue
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93 8 RTS_MODEM yellow
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94 9 GPIO3_DTR green
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95 10 CTS_MODEM orange