SCPA070 june 2023 TCAL6408 , TCAL6416 , TCAL9538 , TCAL9539 , TCAL9539-Q1
- 1
- Abstract
- Trademarks
- 1 Introduction
- 2 Programmable Output Drive Strength
- 3 Programmable Pull-Up or Pull-Down Resistors
- 4 Latchable Inputs
- 5 Maskable Interrupt
- 6 Interrupt Status Register
- 7 Programmable Open-Drain and Push-Pull Outputs
- 8 Benefits of Using TCAL I/O Expanders Versus TCA I/O Expanders
- 9 Summary
- 10References
2 Programmable Output Drive Strength
Agile I/O’s offer programmable output drive strength that allows the I/O pad to be configured to one of four possible current levels. By programming the bits in the Output Drive Strength Registers, the user can adjust the number of transistor pairs that drive the I/O pad. Table 2-1 is from the TCAL6416 data sheet and describes registers 40, 41, 42, and 43 (Output Drive Strength Registers).
| BIT | CC-03 | CC-03 | CC-02 | CC-02 | CC-01 | CC-01 | CC-00 | CC-00 |
| Default | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| BIT | CC-07 | CC-07 | CC-06 | CC-06 | CC-05 | CC-05 | CC-04 | CC-04 |
| Default | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| BIT | CC-13 | CC-13 | CC-12 | CC-12 | CC-11 | CC-11 | CC-10 | CC-10 |
| Default | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| BIT | CC-17 | CC-17 | CC-16 | CC-16 | CC-15 | CC-15 | CC-14 | CC-14 |
| Default | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
Each P-port is assigned exactly 2 bits to configure the drive strength of the output driver. For example, P07 (which is the port 0 GPIO 7) output is configured by two bits located in register 41 called CC-07. Two configurable bits presents four different output current level options which are defined in Table 2-2. The default drive strength for an output pin is 1.00x (CC = 11).
| CC – XX | Output Strength |
|---|---|
| 00 | 0.25x |
| 01 | 0.5x |
| 10 | 0.75x |
| 11 | 1.00x |
The configurable bits for CC-XX determines the number of transistor pairs that are ON at a given time that feed the I/O pad. Figure 2-1 shows the PMOS/NMOS_EN devices that control the push-pull driving pairs that output on P00 – P07 and P10 – P17. Figure 2-1 is a simplified output stage of the p-port.
Figure 2-1 Simplified Output StageReducing output drive strength has a few benefits:
- Weaker outputs slow down the slew rate reducing ringing effects.
- Different pins can have different loading conditions, some can require using the full drive strength while others need weaker drive strength. Thus, each pin can be configured separately where some need the original full drive strength configuration.
- Reduces overall power consumption.