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comparison DUART-cable @ 27:f7ed8c45a8ec

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DUART-cable article written
author Mychaela Falconia <falcon@freecalypso.org>
date Sat, 14 Dec 2019 06:24:24 +0000
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children 78c2cc6ebbb8
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26:1e76655a44bd 27:f7ed8c45a8ec
1 The Calypso chip has two UARTs, called MODEM and IrDA in the chip docs. The
2 primary UART (MODEM) has 4 signals (TxD, RxD, RTS and CTS), whereas the other
3 UART (IrDA) has data leads only (TxD and RxD). TI's C-Sample and D-Sample
4 boards have also established a convention whereby Calypso GPIOs 2 and 3 have
5 been assigned as supplementary modem control signals for the primary MODEM UART,
6 with GPIO 2 being an output from Calypso signaling DCD to the host and with
7 GPIO 3 being an input to Calypso receiving DTR from the host. Note that DSR
8 and RI are still missing in this arrangement.
9
10 In FreeCalypso we have further established our own convention: all FC hardware
11 products that bring out both Calypso UARTs do so by way of a single 10-pin (2x5)
12 2.54 mm header in a fixed pinout given below. This convention was started with
13 FCDEV3B, our first FC hw product, and is now being continued with MMTB1 and
14 other boards. Our standardized DUART header pinout is as follows:
15
16 Header pin Calypso signal
17 1 GND
18 2 GND
19 3 TX_IRDA
20 4 TX_MODEM
21 5 RX_IRDA
22 6 RX_MODEM
23 7 GPIO2_DCD
24 8 RTS_MODEM
25 9 GPIO3_DTR
26 10 CTS_MODEM
27
28 Pins 7 and 9 were originally left unused (they are unconnected on FCDEV3B), but
29 they have been assigned as DCD and DTR (from the host's perspective) starting
30 with MMTB1. Note that while DCD and DTR in the table above are named from the
31 host's perspective, all Calypso signals ending with _MODEM or _IRDA are from
32 the chip's perspective, i.e., the opposite.
33
34 Our standard recommended practice for connecting to our two UARTs from a regular
35 PC or laptop is to use FT2232D breakout boards from the following vendor:
36
37 http://pldkit.com/other/ft2232d-module
38
39 FT2232D is a versatile USB-to-various-things adapter, but in its default
40 configuration which we use here it acts as a bridge from USB to two UARTs,
41 presenting both UARTs behind a single USB device. The breakout board made and
42 sold by PLDkit has two rows of header pins, featuring 15 pins on each side, and
43 the two sides of the board neatly correspond to the A and B sides of FT2232D.
44
45 Our standard recommended method for connecting our two UARTs to a PLDkit FT2232D
46 board is to use a 10-wire ribbon cable that is custom-assembled as follows:
47
48 * One end is terminated with a 10-pin female connector that mates with the DUART
49 header on our modem boards;
50
51 * The other end is split into two parts as described below, and each split end
52 is terminated with a 15-pin female connector that mates with one side of the
53 FT2232D breakout board.
54
55 The split between A and B sides on the FT2232D end is not symmetric, instead 7
56 wires go to side A for the MODEM UART and 3 wires go to side B for the IrDA
57 UART. Assuming the standard color code, the 10-wire ribbon cable gets split
58 between violet and grey wires: brown to violet go to side A, grey to black go
59 to side B. After each wire has been stripped and fitted with a crimp-on female
60 terminal, FT2232D side A wires need to be inserted into the connector housing
61 as follows:
62
63 Wire Pin position FT2232D signal UART signal (host perspective)
64 brown 2 ADBUS0 TxD
65 red 3 ADBUS1 RxD
66 orange 4 ADBUS2 RTS
67 yellow 5 ADBUS3 CTS
68 green 6 ADBUS4 DTR
69 blue 8 ADBUS6 DCD
70 violet 15 GND GND
71
72 FT2232D side B wires need to be inserted into the other connector housing as
73 follows:
74
75 Wire Pin position FT2232D signal UART signal (host perspective)
76 grey 2 BDBUS0 TxD
77 white 3 BDBUS1 RxD
78 black 15 GND GND
79
80 The wires on the other end of the cable (also stripped and fitted with crimp-on
81 female terminals) need to be inserted into another connector housing that will
82 mate with the DUART connector on FreeCalypso modem boards; the pin assignment
83 is as follows:
84
85 Pin position Calypso signal Wire
86 1 GND black
87 2 GND violet
88 3 TX_IRDA white
89 4 TX_MODEM red
90 5 RX_IRDA grey
91 6 RX_MODEM brown
92 7 GPIO2_DCD blue
93 8 RTS_MODEM yellow
94 9 GPIO3_DTR green
95 10 CTS_MODEM orange