Other Parts Discussed in Thread: MSP430G2553
I am unable to get my MSP430G2553 application's MCLK going at 16 MHz using external crystal and a pair of 33 pF loading capacitors (all mounted within 6 mm of the DIP pins. Instead of expected 16 MHz operation, it is running at a very low frequency, under 100 kHz. I have been using sample code snippet from SLAU144H section 5.2.7.1, which includes the instruction "BIS.B #XTS,&BCSCTL1 ; HF mode".
I have selected a 16 MHz crystal as I would like to run the CPU at maximum rated speed and provide a stable source for the internal UART's bit rate generator.
Does the MSP430G2553 basic oscillator system omit the high frequency mode defined in SLAU144H controlled by BCSCTL1 XTS bit? I don't see description a high frequency crystal mode in SLAS375, but the description of the basic clock module in SLAU144H describes the mode.
Should rely on the DCO instead of an external crystal, given that I need to use the internal UART (for simple asynchronous communications)?
My application doesn't need 32 kHz or other low-speed mode - only 16 MHz - as it is not power critical.
Thank you,
Dave
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In SLAS375 (data sheet for MSP430G2553 series) I see this text on the first page:
• Basic Clock Module Configurations
– Internal Frequencies up to 16 MHz With Four Calibrated Frequency
– Internal Very-Low-Power Low-Frequency (LF) Oscillator
– 32-kHz Crystal
– External Digital Clock Source
This text appears later in the same document:
Oscillator and System Clock
The clock system is supported by the basic clock module that includes support for a 32768-Hz watch crystal
oscillator, an internal very-low-power low-frequency oscillator and an internal digitally controlled oscillator (DCO).
The basic clock module is designed to meet the requirements of both low system cost and low power
consumption. The internal DCO provides a fast turn-on clock source and stabilizes in less than 1 μs. The basic
clock module provides the following clock signals:
• Auxiliary clock (ACLK), sourced either from a 32768-Hz watch crystal or the internal LF oscillator.
• Main clock (MCLK), the system clock used by the CPU.
• Sub-Main clock (SMCLK), the sub-system clock used by the peripheral modules.
In SLAU144H in section 5.2.3 this text appears regarding the basic clock module:
The LFXT1 oscillator also supports high-speed crystals or resonators when in HF mode (XTS = 1,
XCAPx = 00). The high-speed crystal or resonator connects to XIN and XOUT and requires external
capacitors on both terminals. These capacitors should be sized according to the crystal or resonator
specifications. When LFXT1 is in HF mode, the LFXT1Sx bits select the range of operation.
Which prevails?
