TMC4671 Datasheet • IC Version V1.00 | Document Revision V1.04 • 2018-Dec-11
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4.2.3 UART Interface
The UART interface is a simple three pin (GND, RxD, TxD) 3.3V UART interface with up to 3 Mbit/s transfer
speed with one start bit, eight data bits, one stop bit, and no parity bits (1N8). The default speed is 9600
bps. Other supported speeds are 115200 bps, 921600 bps, and 3000000 bps.
With an 3.3V-UART-to-USB adapter cable (e.g. FTDI TTL-232R-RPi), the user can use the full maximum data
rate. The UART port enables In-System-Setup-Support by multiple-ported register access.
An UART datagram consists of five bytes - similar to the datagrams of the SPI. In contrast to SPI, the UART
interface has a time out feature. So, the five bytes of a UART datagram need to be send within one second.
A pause of sending more than one second causes a time out and sets the UART protocol handler back into
IDLE state. In other words, waiting for more than one second in sending via UART ensures that the UART
protocol handler is in IDLE state.
A simple UART example (similar to the simple SPI example):
0x81 0x00 0x00 0x00 0x00 // 1st write 0x00000000 into address 0x01 (CHIPINFO_ADDR)
0x00 0x00 0x00 0x00 0x00 // 2nd read register 0x00 (CHIPINFO_DATA), returns 0x34363731
Why UART Interface? It might become necessary during the system setup phase to simply access some
internal registers without disturbing the application, without changing the actual user application software,
and without adding additional debugging code that might disturb the application software itself. The UART
enables this supporting function. In addition, it also enables easy access for monitoring purposes with its
very simple and direct five byte protocol. It is not recommended as standard communication interface due
to low performance.
Figure 10: UART Read Datagram (TMC4671 register read via UART)
Figure 11: UART Write Datagram (TMC4671 register write via UART)
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