Question: When calibrating the internal reference (such as a band gap reference) in PSoC® 1, you may need to bring the reference out to a GPIO pin. However, the analog output buffer would add some offset voltage to any internal analog signal before it is brought out to a GPIO pin. Is there any way to avoid this offset addition, so as to view the exact internally generated reference?
Yes. Bit 1 of the ABF_CR0 register controls whether the analog output buffer is enabled or bypassed. When the analog output buffer is bypassed, you can avoid offset addition while bringing out the internal signal. The operation of this bit is described below. You can also find this information in the PSoC 1 TRM under the ABF_CR0 Register definition.
"Bypass mode connects the analog output driver input directly to the output. When this bit is set, all analog output drivers will be in bypass mode. This is a high impedance connection used primarily for measurement and calibration of internal references. Use of this feature is not recommended for customer designs."