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annotate DUART-cable @ 52:cfe8623b915d

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FC-handset-spec: UART signal pull-up/down documented
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 11 Jun 2021 18:29:06 +0000
parents 78c2cc6ebbb8
children
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1 2020-09 update: we have now produced our own DUART28 adapter that takes the
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2 place of PLDkit FT2232D breakout boards. The article that follows was written
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3 in 2019-12, before our DUART28 was even conceived, and it was written for
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4 PLDkit FT2232D adapters. The new cable that needs to be used with DUART28 is
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5 different: DUART28 brings out a 10-pin header in the same pinout as our Calypso
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6 boards, thus the connection between the two boards becomes a straight-through
78c2cc6ebbb8 DUART-cable: update for DUART28
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7 10-wire ribbon cable.
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8
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9 Original 2019-12 article follows
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10 ================================
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11
27
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12 The Calypso chip has two UARTs, called MODEM and IrDA in the chip docs. The
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13 primary UART (MODEM) has 4 signals (TxD, RxD, RTS and CTS), whereas the other
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14 UART (IrDA) has data leads only (TxD and RxD). TI's C-Sample and D-Sample
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15 boards have also established a convention whereby Calypso GPIOs 2 and 3 have
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16 been assigned as supplementary modem control signals for the primary MODEM UART,
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17 with GPIO 2 being an output from Calypso signaling DCD to the host and with
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18 GPIO 3 being an input to Calypso receiving DTR from the host. Note that DSR
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19 and RI are still missing in this arrangement.
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20
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21 In FreeCalypso we have further established our own convention: all FC hardware
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22 products that bring out both Calypso UARTs do so by way of a single 10-pin (2x5)
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23 2.54 mm header in a fixed pinout given below. This convention was started with
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24 FCDEV3B, our first FC hw product, and is now being continued with MMTB1 and
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25 other boards. Our standardized DUART header pinout is as follows:
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26
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27 Header pin Calypso signal
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28 1 GND
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29 2 GND
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30 3 TX_IRDA
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31 4 TX_MODEM
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32 5 RX_IRDA
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33 6 RX_MODEM
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34 7 GPIO2_DCD
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35 8 RTS_MODEM
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36 9 GPIO3_DTR
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37 10 CTS_MODEM
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38
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39 Pins 7 and 9 were originally left unused (they are unconnected on FCDEV3B), but
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40 they have been assigned as DCD and DTR (from the host's perspective) starting
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41 with MMTB1. Note that while DCD and DTR in the table above are named from the
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42 host's perspective, all Calypso signals ending with _MODEM or _IRDA are from
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43 the chip's perspective, i.e., the opposite.
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44
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45 Our standard recommended practice for connecting to our two UARTs from a regular
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46 PC or laptop is to use FT2232D breakout boards from the following vendor:
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47
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48 http://pldkit.com/other/ft2232d-module
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49
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50 FT2232D is a versatile USB-to-various-things adapter, but in its default
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51 configuration which we use here it acts as a bridge from USB to two UARTs,
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52 presenting both UARTs behind a single USB device. The breakout board made and
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53 sold by PLDkit has two rows of header pins, featuring 15 pins on each side, and
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54 the two sides of the board neatly correspond to the A and B sides of FT2232D.
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55
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56 Our standard recommended method for connecting our two UARTs to a PLDkit FT2232D
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57 board is to use a 10-wire ribbon cable that is custom-assembled as follows:
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58
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59 * One end is terminated with a 10-pin female connector that mates with the DUART
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60 header on our modem boards;
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61
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62 * The other end is split into two parts as described below, and each split end
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63 is terminated with a 15-pin female connector that mates with one side of the
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64 FT2232D breakout board.
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65
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66 The split between A and B sides on the FT2232D end is not symmetric, instead 7
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67 wires go to side A for the MODEM UART and 3 wires go to side B for the IrDA
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68 UART. Assuming the standard color code, the 10-wire ribbon cable gets split
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69 between violet and grey wires: brown to violet go to side A, grey to black go
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70 to side B. After each wire has been stripped and fitted with a crimp-on female
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71 terminal, FT2232D side A wires need to be inserted into the connector housing
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72 as follows:
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73
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74 Wire Pin position FT2232D signal UART signal (host perspective)
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75 brown 2 ADBUS0 TxD
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76 red 3 ADBUS1 RxD
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77 orange 4 ADBUS2 RTS
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78 yellow 5 ADBUS3 CTS
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79 green 6 ADBUS4 DTR
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80 blue 8 ADBUS6 DCD
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81 violet 15 GND GND
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82
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83 FT2232D side B wires need to be inserted into the other connector housing as
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84 follows:
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85
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86 Wire Pin position FT2232D signal UART signal (host perspective)
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87 grey 2 BDBUS0 TxD
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88 white 3 BDBUS1 RxD
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89 black 15 GND GND
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90
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91 The wires on the other end of the cable (also stripped and fitted with crimp-on
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92 female terminals) need to be inserted into another connector housing that will
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93 mate with the DUART connector on FreeCalypso modem boards; the pin assignment
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94 is as follows:
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95
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96 Pin position Calypso signal Wire
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97 1 GND black
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98 2 GND violet
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99 3 TX_IRDA white
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100 4 TX_MODEM red
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101 5 RX_IRDA grey
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102 6 RX_MODEM brown
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103 7 GPIO2_DCD blue
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104 8 RTS_MODEM yellow
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105 9 GPIO3_DTR green
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106 10 CTS_MODEM orange