LPC2101/2/3 FAQ
From K9spud
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Do the GPIO pins have programmable pull-ups?
Doesn't look like it. I can't find any mention of configurable internal pull-up resistors in the user's manual. I just checked my running LPC2103 board and none of the GPIO pins seem to be pulling up despite being configured as inputs.
What do I need to enable the JTAG debugging port?
- RTCK pull up/down?? The example circuits and user's manual seem to have a lot of conflict on which way to pull this signal to enable debugging.
- User's Manual section 20.5: "the pins TMS, TCK, TDI, TDO, and TRST are multiplexed with P0.27 - P0.31. To have them come up as a Debug port, connect a weak bias resistor (4.7K-10K depending on the external JTAG circuitry) between VSS and the RTCK pin. To have them come up as GPIO pins, do not connect a bias resistor, and ensure that any external driver connected to Pin 26 (RTCK) is either driving high or is in high-impedance state during Reset."
- User's Manual section 20.8.1: "For debugging with JTAG pins, RTCK must be HIGH as the RST pin is released (see Figure 66). RTCK may be driven HIGH externally or allowed to float HIGH via its on-chip pull-up."
Keil Software's MCB2103 development board has a pull-down resistor for RTCK. Olimex's development boards has a pull-up resistor for RTCK. Which is correct??
See also this yahoo group posting.
- DBGSEL tied high. When HIGH at Reset, debug mode is entered (User's Manual section 20.4). This pin is an input with internal pull-down (User's Manual section 6.2).
- TCK pull down. Prevent unwanted floating clock signals when no JTAG debugger attached?
- TRST pull up.
- TDI pull up.
- TMS pull up.
