SPRSP85A April 2024 – September 2024 TMS320F28P550SJ , TMS320F28P559SJ-Q1
PRODMIX
Refer to the PDF data sheet for device specific package drawings
Some GPIOs are multiplexed with analog pins and have digital input and output functionality. These are also referred to as AGPIOs. Unlike AIOs, AGPIOs have full input and output capability. By default, the AGPIOs are not connected and must be configured. Table 5-7 shows how to configure the AGPIOs. To enable the analog functionality, set the register AGPIOCTRLx from analog subsystem. To enable the digital functionality, set the register GPxAMSEL from the General-Purpose Input/Output (GPIO) chapter.
AGPIOCTRLx.GPIOy (Default = 0) |
GPxAMSEL.GPIOy (Default = 1) |
Pin Connected To: | |
---|---|---|---|
ADC | GPIOy | ||
0 | 0 | - | Yes |
0 | 1 | -(1) | -(1) |
1 | 0 | - | Yes |
1 | 1 | Yes | - |
The general schematic of analog subsystem with AGPIO implementation is illustrated in Figure 5-6. The combinations of use cases for a specific analog input pin need special consideration are shown in Table 5-8. The AGPIO analog pin path contains an extra series switch of 53Ω. This creates a low capacitance isolated node shared by the ADC and CMPSS Comparator as shown in Figure 5-6. This node can be disturbed when the ADC samples the channel (depending on the prior voltage stored on the ADC sample and hold capacitor), and this disturbance can cause a false CMPSS event of up to 50ns. As shown in Table 5-8, special considerations or workarounds need to be used for the combination of CMPSS Input, ADC Sampling, and AGPIO. To accommodate this potential disturbance the following workarounds can be implemented:
Function Used on a Specific Analog Pin | Component Used | ||||
---|---|---|---|---|---|
CMPSS Comparator Input | Yes | - | Yes | - | Yes |
ADC Sampling | Yes | Yes | - | Yes | Yes |
AGPIO Analog Pin Type | Yes | Yes | Yes | - | - |
AIO Analog Pin Type | - | - | - | Yes | Yes |
Result | Workaround needed | No special analysis or workaround needed |