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add gps pinout notes
*[https://web.archive.org/web/20200914132431/https://www.st.com/resource/en/programming_manual/cd00004617-st7-family-icc-protocol-reference-manual-stmicroelectronics.pdf ST7 Family ICC Protocol Reference Manual]
*With a buffered 16MHz clock provided by Y3/U12, possible CPU speeds are 8MHz(/1), 4MHz(/2), 2MHz(/4), 1MHz(/8) depending on MCC configuration.
*Instruction timings have yet to be found. The datasheet only says '2-12 cycles per instruction', and a note from Raisonance support says that NOP does indeed take 2 cycles. These will be needed before we can bring up a bit-banged software debug UART as well as the bitstream for the CC1050, and may need to be reverse engineered via GPIO+oscilloscope.
''U4 - (Marked Z252)''
==GPS Subsystem==
Trimble 63530 baud rate is 38400, 5V, connected to ST7 SCI port(Pins 1&2 on ST7, TDO and RDI). Assuming 8N1 framing, this means interrupts must not be disabled for >260 microseconds or else bytes may be lost as the receive shift register overflows.
{| class="wikitable"
|+
!GPS
Pin
!GPS
Name
!Goes to
!
|-
|1
|GND
|ground
|
|-
|2
|GND
|ground
|
|-
|3
|RF-IN
|Passives, then GPS antenna
|
|-
|4
|GND
|ground
|
|-
|5
|LNA
|nothing visible
|
|-
|6
|VBAT
|nothing visible
|
|-
|7
|Open
|internal via to somewhere - should be low
|
|-
|8
|Short
|VCC3 - should be high
|
|-
|9
|Reserved
|VCC3
|
|-
|10
|Reserved
|VCC3
|
|-
|11
|Xreset
|VCC3
|
|-
|12
|Vcc
|VCC3
|
|-
|13
|GND
|ground
|
|-
|14
|GND
|ground
|
|-
|15
|GND
|ground
|
|-
|16
|Xstandby
|VCC3
|
|-
|17
|Reserved
|nothing visible
|
|-
|18
|Reserved
|nothing visible
|
|-
|19
|PPS
|Via to back to trace to via to small via connected to R3, then trace to 47k to ground, then some pins on U2 - looks like a level translator - through that then to a hidden via, pops back up at TP36 which is connected to PB4 on the ST7.
|
|-
|20
|RXD-B
|appears unused
|
|-
|21
|RXD-A
|comes from U4 level translator, splits to pin 24 on edge connector then 10k resistor to Pin16 on ST7 which is PF1
|
|-
|22
|Reserved
|
|
|-
|23
|TXD-A
|38400 baud to the ST7 RDI/Pin1/PE1
|
|-
|24
|TXD-B
|4800 baud appears unused
|
|-
|25
|Reserved
|
|
|-
|26
|Reserved
|
|
|-
|27
|GND
|ground
|
|-
|28
|GND
|ground
|
|}
GPS xSTANDBY - connected to 3.3v
GPS xRESET - connected to 3.3v
==Test Points==
