FreeCalypso > hg > freecalypso-schem2

annotate venus/doc/MEMIF-fixed-2.8V @ 94:4502eec1e805

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D405: use Nexperia part sourced from Digi-Key direct The previously selected part was from a Digi-Key marketplace vendor, and they seem to not actually have that part, as the order has been in limbo for over a month - so I put in the time and effort to look around, and found a readily available equivalent part from Nexperia.
author Mychaela Falconia <falcon@freecalypso.org>
date Tue, 11 Jan 2022 19:11:22 +0000
parents 711358516b55
children
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37
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
1 Our Calypso+Iota chipset allows Calypso MEMIF (memory bus interface) to run at
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
2 either 2.8V or 1.8V; the choice between these two voltages is made by way of
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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3 Iota VLMEM pin strapping. TI's Leonardo reference design had a pair of resistor
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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4 footprints connected to VLMEM (R209 pull-up for 2.8V and R210 pull-down for
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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5 1.8V), and both of these resistor footprints have been preserved by both
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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6 Openmoko and iWOW. Our FCDEV3B, based on Openmoko, has them too. All 3 boards
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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7 in question (OM GTA01/02, FCDEV3B and TR-800 module) use flash+RAM MCPs that run
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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8 at 2.8V, thus R209 is populated, R210 is unpopulated, and MEMIF runs at 2.8V.
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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9
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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10 On FC Venus we have an additional complication: Calypso MEMIF goes not only to
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
11 the flash+RAM MCP, but also to our big color LCD. On the one hand our LCD
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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12 module does support split power supplies, with Vccio supporting the full range
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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13 from 1.65 to 3.6 V, and we could design our board to support both MEMIF voltage
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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14 options and thus both our current 2.8V flash+RAM MCP and hypothetical 1.8V
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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15 options. However, this design would imply additional complexity and cost:
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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16
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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17 * We would need to run two power supply traces to our LCD: one trace to the LCD
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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18 module's Vcc pin (needs to be 2.5 V minimum) from our Vio rail (always 2.8V),
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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19 and another trace to the LCD module's Vccio pin from Iota VRMEM or VRRAM
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
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20 regulator output (voltage switches with VLMEM strapping).
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
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21
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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22 * Because Calypso nRESET_OUT, which we use for LCD reset, is a 2.8V output
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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23 (V-IO domain, not MEMIF), we would need to insert a dual supply translating
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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24 buffer between this Calypso output and the LCD module's reset input.
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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25
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
26 However, because the hypothetical possibility of swapping our current 2.8V
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
27 flash+RAM MCP for a 1.8V part is just that, hypothetical and not realistic, the
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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28 Mother's decision is to simplify our Venus board design by fixing MEMIF at 2.8V.
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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29 The simplifications resulting from this decision are as follows:
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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30
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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31 * R209 and R210 are eliminated, Iota VLMEM is tied directly to UPR.
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
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32
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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33 * Only one 2.8V power supply trace will need to run to the LCD module; because
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
34 the module's Vcc and Vccio pins are directly adjacent on the FPC tail
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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35 interface, a single trace supplying both pins will be ideal.
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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36
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
37 * No extra buffer IC on the connection from Calypso nRESET_OUT to the LCD
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
38 module's reset input, just a direct trace.
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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39
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
40 * 2.8V supply for the LCD will be sourced from Vio (not VRMEM or VRRAM),
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
41 matching our previous Luna platform in which only Vio is available.
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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42
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
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43 When it comes to the flash+RAM MCP, we are being deliberately non-innovative:
9c2f913fa5cf venus/doc/MEMIF-fixed-2.8V: explanatory article
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
44 rather than explore potentially suitable parts on our own, we copy specific
91
711358516b55 venus/doc/MEMIF-fixed-2.8V: update for new MCP
Mychaela Falconia <falcon@freecalypso.org>
parents: 37
diff changeset
45 parts that have been used successfully in historical Calypso designs. Our PCB
711358516b55 venus/doc/MEMIF-fixed-2.8V: update for new MCP
Mychaela Falconia <falcon@freecalypso.org>
parents: 37
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46 footprint for flash+RAM MCP is compatible with Spansion S71PL064J, S71PL129J
711358516b55 venus/doc/MEMIF-fixed-2.8V: update for new MCP
Mychaela Falconia <falcon@freecalypso.org>
parents: 37
diff changeset
47 and S71PL129N families, and all of our potential MCP choices require a single
711358516b55 venus/doc/MEMIF-fixed-2.8V: update for new MCP
Mychaela Falconia <falcon@freecalypso.org>
parents: 37
diff changeset
48 supply between 2.7 and 3.1 V, hence 2.8V MEMIF.