aboutsummaryrefslogtreecommitdiffstats
path: root/source/hardware/maple.rst
blob: 610fdfcae4b4fac033a4912ba5c59e0f91b3b36d (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
.. highlight:: sh

.. _maple:

Maple
=====

This page is a general resource for information specific to the Maple.

.. contents:: Contents
   :local:

.. TODO [dma.rst] Ref to dma.rst in sequel instead of libmaple-dma
.. TODO [nvic.rst] Ref to nvic.rst in sequel

Technical Specifications
------------------------

* MCU: :ref:`STM32F103RBT6 <maple-stdocs>`, a 32-bit ARM Cortex M3
  microprocessor
* Clock Speed: **72 MHz**
* **128 KB Flash** and **20 KB SRAM**
* 43 :ref:`digital I/O pins (GPIOs) <gpio>`
* 15 :ref:`PWM <pwm>` pins at 16 bit resolution
* 15 :ref:`analog input (ADC) <adc>` pins at 12-bit resolution
* 2 :ref:`SPI <spi>` peripherals
* 2 :ref:`I2C <i2c>` peripherals
* 7 Channels of Direct Memory Access (**DMA**) (:ref:`libmaple-dma`)
* 3 :ref:`USART (serial port) <usart>` peripherals
* One advanced and three general-purpose :ref:`timers <timers>`
* Dedicated :ref:`USB <usb>` port for programming and communications
* :ref:`JTAG <jtag>`
* Nested Vectored Interrupt Controller (NVIC) (including
  :ref:`external interrupt <external-interrupts>` on GPIOs)
* Supplies up to 500 mA at 3.3 V, with separate 250 mA digital and
  analog regulators for low-noise analog performance
* :ref:`Open source, four layer design <maple-hardware>`
* Support for low power, sleep, and standby modes (<500 μA)
* Operating Voltage: 3.3 V
* Input Voltage (recommended): 4 V — 12 V
* Dimensions: 2.05″ × 2.1″

.. _maple-identify-rev:

Identifying your Rev
--------------------

We went through three versions ("Revs") of the Maple hardware: Rev 1,
Rev 3, and Rev 5 [#frev2_4]_; Rev 5, the final design, is currently on
sale.  The following sections will help you to help you identify your
Rev.

Rev 5
^^^^^

These boards went on sale in November 2010.  They have white buttons
and "r5" in small print near the "LeafLabs Maple" text next to the
"infinity leaf" logo.  The Maple Rev 5 repositioned the double header
on the right hand side to better fit 0.1 inch pitch breadboard.  This
necessitated the removal of pins 21 and 22 from the double header;
they are still available, but don't have any headers installed on
them.

.. figure:: /_static/img/maple_rev5.png
   :align: center
   :alt: Maple Rev 5

Rev 3
^^^^^

This batch of boards went on sale beginning in May 2010. They have a
darker red silkscreen and the "infinity leaf" logo.  The Maple Rev 3
was the first version which includes the built-in button, labeled BUT.

.. figure:: /_static/img/maple_rev3.png
   :align: center
   :alt: Maple Rev 3

Rev 1
^^^^^

A small number of Maple Rev 1 boards went on sale in late 2009.  They
have a light red silkscreen and a single pixelated leaf as a logo.

.. figure:: /_static/img/maple_rev1.png
   :align: center
   :alt: Maple Rev 1

.. _maple-powering:

Powering the Maple
------------------

The Maple's power source is determined by the header to the left of
the "LeafLabs" label on the silkscreen.  All versions of the Maple can
be powered from the barrel jack connector, USB, or a LiPo battery.  We
ship the Maple with a jumper on the USB selector.  In order to power
it off of an alternative source, unplug the Maple, then move the
jumper to the desired selector before reconnecting power.

You can also power the Maple via the pin labeled "Vin" on the lower
header.  This pin feeds into both the digital and analog voltage
regulators.  However, don't do this while simultaneously powering the
board from another source, or you could damage it.

.. warning:: Silkscreens on Maples up through Rev 5s manufactured in
   Spring 2011 falsely indicated that the barrel jack could be
   supplied by up to 18 V.  We recommend a barrel jack input voltage
   **no greater than 12 V**.

   Rev5s manufactured after Spring 2011 may still have this error on
   the silk, but it has been marked over.

   See :ref:`this erratum <maple-barrel-jack>` for more information.

Using the Built-in Battery Charger
----------------------------------

Maples Rev 3 and Rev 5 also have a built-in LiPo battery charger.  In
order to use it, put a jumper across the CHRG header on the power
selection header and across the USB, or EXT selectors, depending on
whether you're charging the battery via USB cable or barrel jack
connector.  The LED labeled CHRG will light up while the battery is
being charged.  When the battery is finished charging, the LED labeled
DONE will light up.

.. _maple-gpios:

GPIO Information
----------------

The Maple features 38 ready-to-use general purpose input/output (see
:ref:`gpio`) pins for digital input/output, numbered ``D0`` through
``D37``.  These numbers correspond to the numeric values next to each
header on the Maple silkscreen.

.. _maple-ret6-but:

Pin ``D38`` is the board's :ref:`button pin <lang-board-values-but>`.
It is thus mainly useful as an :ref:`input <lang-pin-levels>`.  The
pin will :ref:`read <lang-digitalread>` ``HIGH`` when the :ref:`button
is pressed <lang-isbuttonpressed>`.

More GPIOs (numbered ``D39``\ --``D42`` on the back of the Maple's
silkscreen) are available if you use the :ref:`lang-disabledebugports`
function; see the :ref:`board-specific debug pin constants
<lang-board-values-debug>` for more information.  (See :ref:`this
erratum <maple-nrst-pb4>` for information about the pin numbered
``43`` on the silkscreen).

.. TODO [0.1.0] silkscreen pictures which expand abbreviations

.. _maple-pin-map-master:

Master Pin Map
^^^^^^^^^^^^^^

This table shows a summary of the available functionality on every
GPIO pin, by peripheral type.  The "5 V?" column documents whether or
not the pin is :ref:`5 volt tolerant <gpio-5v-tolerant>`.

Note that this table is not exhaustive; on some pins, more peripherals
are available than are listed here.

.. csv-table::
   :header: Pin, :ref:`GPIO <gpio>`, :ref:`ADC <adc>`, :ref:`Timer <timers>`, :ref:`I2C <i2c>`, :ref:`UART <usart>`, :ref:`SPI <spi>`, 5 V?

   D0,  PA3,  CH3,  2_CH4,     -,       2_RX,  -,      -
   D1,  PA2,  CH2,  2_CH3,     -,       2_TX,  -,      -
   D2,  PA0,  CH0,  2_CH1_ETR, -,       2_CTS, -,      -
   D3,  PA1,  CH1,  2_CH2,     -,       2_RTS, -,      -
   D4,  PB5,  -,    -,         1_SMBA,  -,     -,      -
   D5,  PB6,  -,    4_CH1,     1_SCL,   -,     -,      Yes
   D6,  PA8,  -,    1_CH1,     -,       1_CK,  -,      Yes
   D7,  PA9,  -,    1_CH2,     -,       1_TX,  -,      Yes
   D8,  PA10, -,    1_CH3,     -,       1_RX,  -,      Yes
   D9,  PB7,  -,    4_CH2,     1_SDA,   -,     -,      Yes
   D10, PA4,  CH4,  -,         -,       2_CK,  1_NSS,  -
   D11, PA7,  CH7,  3_CH2,     -,       -,     1_MOSI, -
   D12, PA6,  CH6,  3_CH1,     -,       -,     1_MISO, -
   D13, PA5,  CH5,  -,         -,       -,     1_SCK,  -
   D14, PB8,  -,    4_CH3,     -,       -,     -,      Yes
   D15, PC0,  CH10, -,         -,       -,     -,      -
   D16, PC1,  CH11, -,         -,       -,     -,      -
   D17, PC2,  CH12, -,         -,       -,     -,      -
   D18, PC3,  CH13, -,         -,       -,     -,      -
   D19, PC4,  CH14, -,         -,       -,     -,      -
   D20, PC5,  CH15, -,         -,       -,     -,      -
   D21, PC13, -,    -,         -,       -,     -,      -
   D22, PC14, -,    -,         -,       -,     -,      -
   D23, PC15, -,    -,         -,       -,     -,      -
   D24, PB9,  -,    4_CH4,     -,       -,     -,      Yes
   D25, PD2,  -,    3_ETR,     -,       -,     -,      Yes
   D26, PC10, -,    -,         -,       -,     -,      Yes
   D27, PB0,  CH8,  3_CH3,     -,       -,     -,      -
   D28, PB1,  CH9,  3_CH4,     -,       -,     -,      -
   D29, PB10, -,    -,         2_SCL,   3_TX,  -,      Yes
   D30, PB11, -,    -,         2_SDA,   3_RX,  -,      Yes
   D31, PB12, -,    -,         2_SMBA,  3_CK,  2_NSS,  Yes
   D32, PB13, -,    -,         -,       3_CTS, 2_SCK,  Yes
   D33, PB14, -,    -,         -,       3_RTS, 2_MISO, Yes
   D34, PB15, -,    -,         -,       -,     2_MOSI, Yes
   D35, PC6,  -,    -,         -,       -,     -,      Yes
   D36, PC7,  -,    -,         -,       -,     -,      Yes
   D37, PC8,  -,    -,         -,       -,     -,      Yes
   D38, PC9,  -,    -,         -,       -,     -,      Yes
   D39, PA13, -,    -,         -,       -,     -,      Yes
   D40, PA14, -,    -,         -,       -,     -,      Yes
   D41, PA15, -,    -,         -,       -,     -,      Yes
   D42, PB3,  -,    -,         -,       -,     -,      Yes

.. _maple-gpio-port-map:

GPIO Port Pin Map
^^^^^^^^^^^^^^^^^

The following table shows what pins are associated with each
:ref:`GPIO port <gpio-ports>`.

.. csv-table::
   :header: GPIOA, GPIOB, GPIOC

   PA0: D2,   PB0:  D27, PC0: D15
   PA1: D3,   PB1:  D28, PC1: D16
   PA2: D1,   PB2:  -,   PC2: D17
   PA3: D0,   PB3:  D42, PC3: D18
   PA4: D10,  PB4:  D43, PC4: D19
   PA5: D13,  PB5:  D4,  PC5: D20
   PA6: D12,  PB6:  D5,  PC6: D35
   PA7: D11,  PB7:  D9,  PC7: D36
   PA8: D6,   PB8:  D14, PC8: D37
   PA9: D7,   PB9:  D24, PC9: D38
   PA10: D8,  PB10: D29, PC10: D26
   PA11: -,   PB11: D30, PC11: -
   PA12: -,   PB12: D31, PC12: -
   PA13: D39, PB13: D32, PC13: D21
   PA14: D40, PB14: D33, PC14: D22
   PA15: D41, PB15: D34, PC15: D23

.. _maple-timer-map:

Timer Pin Map
^^^^^^^^^^^^^

The following table shows what pins are associated with a particular
timer's capture/compare channels.

.. csv-table::
   :header: Timer, Ch. 1, Ch. 2, Ch. 3, Ch. 4
   :delim: |

   1 | D6  | D7  | D8  | -
   2 | D2  | D3  | D1  | D0
   3 | D12 | D11 | D27 | D28
   4 | D5  | D9  | D14 | D24

.. _maple-exti-map:

EXTI Line Pin Map
^^^^^^^^^^^^^^^^^

The following table shows which pins connect to which :ref:`EXTI lines
<external-interrupts-exti-line>` on the Maple.

.. list-table::
   :widths: 1 1
   :header-rows: 1

   * - EXTI Line
     - Pins
   * - EXTI0
     - D2, D15, D27
   * - EXTI1
     - D3, D16, D28
   * - EXTI2
     - D1, D17, D25
   * - EXTI3
     - D0, D18, D42
   * - EXTI4
     - D10, D19
   * - EXTI5
     - D4, D13, D20
   * - EXTI6
     - D5, D12, D35
   * - EXTI7
     - D9, D11, D36
   * - EXTI8
     - D6, D14, D37
   * - EXTI9
     - D7, D25, D28
   * - EXTI10
     - D8, D26, D29
   * - EXTI11
     - D30
   * - EXTI12
     - D31
   * - EXTI13
     - D21, D32, D39
   * - EXTI14
     - D22, D33, D40
   * - EXTI15
     - D23, D34, D41

.. _maple-usart-map:

USART Pin Map
^^^^^^^^^^^^^

The Maple has three serial ports (also known as :ref:`USARTs
<usart>`): ``Serial1``, ``Serial2``, and ``Serial3``. They communicate
using the pins given in the following table.

.. csv-table::
   :header: Serial Port, TX, RX, CK, CTS, RTS
   :delim: |

   ``Serial1`` | D7  | D8  | D6  |     |
   ``Serial2`` | D1  | D0  | D10 | D2  | D3
   ``Serial3`` | D29 | D30 | D31 | D32 | D33

.. _maple-adc-bank:

Low-Noise ADC Pins
^^^^^^^^^^^^^^^^^^

The six pins at the bottom right of the board (D15—D20) generally
offer lower-noise ADC performance than other pins on the board. If
you’re concerned about getting good ADC readings, we recommend using
one of these pins to take your measurements.

Maple has an electrically isolated analog power plane with its own
regulator, and a geometrically isolated ground plane. Pins D15—D20 are
laid out to correspond with these analog planes, and our measurements
indicate that they generally have the lowest noise of all the analog
lines.  However, analog performance may vary depending upon the
activity of the other GPIOs.  Consult the :ref:`Maple hardware design
files <maple-hardware>` for more details.

Board-Specific Values
---------------------

This section lists the Maple's :ref:`board-specific values
<lang-board-values>`.

- ``CYCLES_PER_MICROSECOND``: 72
- ``BOARD_BUTTON_PIN``: 38
- ``BOARD_LED_PIN``: 13
- ``BOARD_NR_GPIO_PINS``: 44 (however, :ref:`pin D43 is not usable
  <maple-nrst-pb4>`)
- ``BOARD_NR_PWM_PINS``: 15
- ``boardPWMPins``: 0, 1, 2, 3, 5, 6, 7, 8, 9, 11, 12, 14, 24, 27, 28
- ``BOARD_NR_ADC_PINS``: 15
- ``boardADCPins``: 0, 1, 2, 3, 10, 11, 12, 15, 16, 17, 18, 19, 20, 27, 28
- ``BOARD_NR_USED_PINS``: 7
- ``boardUsedPins``: ``BOARD_LED_PIN``, ``BOARD_BUTTON_PIN``,
  ``BOARD_JTMS_SWDIO_PIN``, ``BOARD_JTCK_SWCLK_PIN``,
  ``BOARD_JTDI_PIN``, ``BOARD_JTDO_PIN``, ``BOARD_NJTRST_PIN``
- ``BOARD_NR_USARTS``: 3
- ``BOARD_USART1_TX_PIN``: 7
- ``BOARD_USART1_RX_PIN``: 8
- ``BOARD_USART2_TX_PIN``: 1
- ``BOARD_USART2_RX_PIN``: 0
- ``BOARD_USART3_TX_PIN``: 29
- ``BOARD_USART3_RX_PIN``: 30
- ``BOARD_NR_SPI``: 2
- ``BOARD_SPI1_NSS_PIN``: 10
- ``BOARD_SPI1_MOSI_PIN``: 11
- ``BOARD_SPI1_MISO_PIN``: 12
- ``BOARD_SPI1_SCK_PIN``: 13
- ``BOARD_SPI2_NSS_PIN``: 31
- ``BOARD_SPI2_MOSI_PIN``: 34
- ``BOARD_SPI2_MISO_PIN``: 33
- ``BOARD_SPI2_SCK_PIN``: 32
- ``BOARD_JTMS_SWDIO_PIN``: 39
- ``BOARD_JTCK_SWCLK_PIN``: 40
- ``BOARD_JTDI_PIN``: 41
- ``BOARD_JTDO_PIN``: 42
- ``BOARD_NJTRST_PIN``: :ref:`43 <maple-nrst-pb4>`

.. _maple-hardware:

Hardware Design Files
---------------------

The hardware schematics and board layout files are available in the
`Maple GitHub repository <https://github.com/leaflabs/maple>`_.  The
design files for Rev 1, Rev 3, and Rev 5 are respectively in the
``maple-r1``, ``maple-r3``, and ``maple-r5`` subdirectories.  A
schematic for a JTAG adapter suitable for use with Maple is available
in the ``jtagadapter`` directory.

From the GitHub repository main page, you can download the entire
repository by clicking the "Download" button.  If you are familiar
with `Git <http://git-scm.com/>`_, you can also clone the repository
at the command line with ::

    $ git clone git://github.com/leaflabs/maple.git

.. _maple-failure-modes:

Failure Modes
-------------

The following are known failure modes.  The failure modes aren't
design errors, but are easy ways to break or damage your board
permanently.

* **High voltage on non-tolerant pins**: not all header pins are 5V
  compatible; so e.g. connecting certain serial devices in the wrong
  way could over-voltage the pins.  The :ref:`pin-mapping master table
  <maple-pin-map-master>` details which pins are :ref:`5 V tolerant
  <gpio-5v-tolerant>`.

Errata
------

This section documents design flaws and other errors.

General
^^^^^^^

.. _maple-barrel-jack:

* **Barrel jack power supply voltage mistake**: The acceptable voltage
  range given next to the barrel jack on the Maple through Rev 5s
  manufactured in Spring 2011 is **incorrect**.  The given range is 7
  V — 18 V.  In fact, **18 V is too high** and should not be supplied
  to your board.  The recommended maximum voltage you should apply is
  **12 V**.

  The original voltage regulators used on the Maple were rated up to
  18 V.  However, the voltage regulators on current Maple Revs are
  rated up to 16 V.  Our tests indicate that they operate correctly
  through 12 V.  We do not recommend higher input voltages.

.. _maple-nrst-pb4:

* **Reset and PB4 tied together**: The Maple's reset line is also
  connected to PB4, which is labeled on the silkscreen as pin 43.
  Thus, attempting to use pin 43 as a GPIO can reset your board.  This
  has other implications.  Since PB4 is also the JTAG NJTRST line,
  this prevents the :ref:`JTAG <jtag>` "reset halt" command from
  working properly.

.. _maple-power-supply:

* **Power supply marketing mistake**: We originally sold the Maple
  advertising that it was capable of supplying up to 800 mA; the
  correct value is 500 mA.

.. _maple-pwm-marketing:

* **PWM marketing mistake**: We originally advertised the Maple as
  having 22 PWM-capable pins; the correct number is 15.

.. _maple-adc-marketing:

* **ADC marketing mistake**: We originally advertised the Maple as
  having 16 analog input pins.  Due to :ref:`the following issue
  <maple-adc-led>`, the correct number is 15.

.. _maple-adc-led:

* **ADC on BOARD_LED_PIN**: We originally sold the Maple RET6 Edition
  advertising 16 analog input lines.  However, one of them (the one on
  pin 13) is also connected to the built-in LED.  The voltage drop
  across the LED means that the analog to digital converter on that
  pin is not really useful.  While it is still usable, its readings
  will be incorrect.


By Rev
^^^^^^

The following subsections lists known issues and warnings for each
revision of the Maple board.

Rev 5
~~~~~

* **Pin 3 AIN missing**: Pin 3 is capable of analog input, but on Rev
  5s manufactured during Fall 2010, the corresponding "AIN" is missing
  from its silkscreen.  This mistake was fixed in later manufacturing
  runs.

Rev 3
~~~~~

* **Pin 3 AIN missing**: Pin 3 is capable of analog input, but the
  corresponding "AIN" is missing from the Rev 3 silkscreen.

.. _maple-rev3-bad-buttons:

* **Bad/Sticky Buttons**: a number of Rev 3 boards sold in May-June 2010
  have questionable RESET and BUT buttons.

  What seems to have happened is that the flux remover we used to
  clean the boards before shipping eroded the plastic internals, which
  resulted in intermittent functionality. All buttons on all shipped
  boards did function in testing, but some may have been unreliable in
  regular use.

  If you have this problem, we will be happy to ship you new buttons
  if you think you can re-solder them yourself, or you can ship us
  your board and we will swap out that part.

  For reference, the button part number is KMR211GLFS and the flux
  remover we used is "Precision Electronics Cleaner" from RadioShack,
  which is "Safe on most plastics" and contains: dipropylene glycol
  monomethyl ether, hydrotreated heavy naphtha, dipropylene glycol
  methyl ether acetate (say that three times fast!), and carbon
  dioxide.

* **Resistors on pins 0 and 1**: these header pins, which are RX/TX on
  USART2 (:ref:`Serial2 <lang-serial>`), have resistors in-line
  between the STM32 and the headers. These resistors increase the
  impedance of the lines for ADC reads and affect the open drain GPIO
  functionality of the pins.

  These resistors were accidentally copied over from older Arduino USB
  designs, where they appear to protect the USB-Serial converter from
  TTL voltage on the headers.

* **Silkscreen Errors**: the silkscreen on the bottom indicated PWM
  functionality on pin 25 and listen the external header GND pin as
  number 38 (actually 38 is connected to the BUT button). We manually
  sharpied over both of these mistakes.

Rev 1
~~~~~

* **ADC noise**: generally very high, in particular when the USB port
  is being used for communications (including keep-alive pings when
  connected to a computer).

  This issue was resolved in Rev 3 with a 4-layer design and a
  :ref:`geometrically isolated ADC Vref plane <maple-adc-bank>`.

* **Resistors on pins 0 and 1**: these header pins, which are RX/TX on
  USART2 (:ref:`Serial2 <lang-serial>`), have resistors in-line
  between the STM32 and the headers. These resistors increase the
  impedance of the lines for ADC reads and affect the open drain GPIO
  functionality of the pins.

  These resistors were accidentally copied over from older Arduino USB
  designs, where they appear to protect the USB-Serial converter from
  TTL voltage on the headers.

* **Silkscreen Differences**: the pin numbering scheme on Rev 1 is
  different from Rev 3, and thus Rev 3 software is difficult to use
  with Rev 1 boards. Notably, the analog input bank is labeled A0-A4
  on Rev 1 but 15-20 on Rev 3, and the extra header bank does not have
  a pinout table on the bottom.

* **No BUT Button**: the BUT button, useful for serial bootloading,
  was only added in Rev 3. As a workaround, you can directly short the
  appropriate MCU pin to Vcc; see `this forum posting
  <http://forums.leaflabs.com/topic.php?id=32#post-126>`_.

Recommended Reading
-------------------

.. _maple-stdocs:

STMicro documentation for STM32F103RB microcontroller:

* `Datasheet
  <http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00161566.pdf>`_
  (PDF); covers STM32F103x8, STM32F103xB.
* `Reference Manual RM0008
  <http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/REFERENCE_MANUAL/CD00171190.pdf>`_
  (PDF); definitive resource for peripherals on the STM32F1 line.
* `Programming Manual PM0056
  <http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/PROGRAMMING_MANUAL/CD00228163.pdf>`_
  (PDF); assembly language and register reference.
* `STM32F103RB <http://www.st.com/internet/mcu/product/164487.jsp>`_
  overview page with links to further references.

.. rubric:: Footnotes

.. [#frev2_4] Revs 2 and 4 were prototypes that didn't pass internal
   testing.