SC16IS75x Breakout Boards

This is a collection of very simple and often copied breakout boards as Zephyr shield based on the NXP SC16IS750 [9] or SC16IS752 [11] chip, a bridge from an I2C or SPI bus to a single or dual channel UART with integrated GPIO controller. The origin of all breakout boards was the BOB-09981 [4] (BOB-09745 [7]) design from SparkFun with the single-channel UART/GPIO bridge. This is available both as a one-to-one clone and as a modified version with a two-channel UART/GPIO bridge from CJMCU (Changjiang Intelligent Technology Co., Ltd.) [1] or Q-Baihe (Wuhan Lilly Electronics Co., Ltd.) [2].

Operation and connection

All breakout boards contain only the essential components required to operate the bridge IC. These are a crystal for clock provision, blocking capacitors, important pull-up resistors and a small 3.3V power supply. Any additional circuits or components required must be provided externally. The single channel UART/GPIO breakout boards use the NXP SC16IS750 [9]. The dual channel UART/GPIO breakout boards use the NXP SC16IS752 [11]. The user is free to select either an I2C or an SPI bus to operate with the bridge IC. The selection is made via the pin labeled I2C/SPI on one of the headers. See figures below.

All bridge ICs are interrupt-capable (/IRQ) and can be reset by a hardware reset (/RESET). Breakout boards with a SC16IS750 (single channel) have a crystal with a fixed frequency of 14.7456MHz. Breakout boards with a SC16IS752 (dual channel) have a crystal with a fixed frequency of 1.8432MHz.

SPI bus operation

The SC16IS750 or SC16IS752 works in SPI bus operation mode when I2C/SPI set to Low.

SC16IS750 on SPI bus	SC16IS752 on SPI bus

Multiple bridge ICs can be used by connecting the SPI /CS signal to different outputs of the SPI host controller.

Note

Despite what may be printed on the PCB, when using the SC16IS750 or SC16IS752 in SPI mode, the SDA pin should be held low or open, not high. Otherwise, interrupt handling may not function correctly.

I2C bus operation

The SC16IS750 or SC16IS752 works in I2C bus operation mode when I2C/SPI set to High.

SC16IS750 on I2C bus	SC16IS752 on I2C bus

Multiple bridge ICs can be operated on a single I2C host controller by correctly wiring the I2C address select pins A0 and A1. See the following table.

I2C address selection.

A1	A2	raw address	8-bit address	7-bit address (shifted)
VDD	VDD	1001 000X	0x90	0x48
VDD	VSS	1001 001X	0x92	0x49
VDD	SCL	1001 010X	0x94	0x4A
VDD	SDA	1001 011X	0x96	0x4B
VSS	VDD	1001 100X	0x98	0x4C
VSS	VSS	1001 101X	0x9A	0x4D
VSS	SCL	1001 110X	0x9C	0x4E
VSS	SDA	1001 111X	0x9E	0x4F
SCL	VDD	1010 000X	0xA0	0x50
SCL	VSS	1010 001X	0xA2	0x51
SCL	SCL	1010 010X	0xA4	0x52
SCL	SDA	1010 011X	0xA6	0x53
SDA	VDD	1010 100X	0xA8	0x54
SDA	VSS	1010 101X	0xAA	0x55
SDA	SCL	1010 110X	0xAC	0x56
SDA	SDA	1010 111X	0xAE	0x57

Supported Shields

Single-channel UART/GPIO bridge

SparkFun BOB-09745SparkFun BOB-09981CJMCU-750Q-Baihe GT-SC16IS750

OBSOLETE and UNSUPPORTED, use BOB-09981 instead!

The BOB-09745 [7] is the original breakout board from SparkFun in the early first revision v1.2 with a 12.2880MHz crystal. This revision is not supported by this shield abstraction, as a crystal is populated with an unsuitable value!

• BOB-09745 Schematic [8]

• Git: https://github.com/sparkfun/SC16IS750_Breakout/tree/v_1.3

• SC16IS750 Datasheet [10]

Warning

The board contains a design defect resulting in the interrupt pin (/IRQ) of the SC16IS750 not being physically connected to the board outputs.

See also: https://github.com/sparkfun/SC16IS750_Breakout/issues/1

However, this error can be fixed by soldering a small wire bridge from pin 11 (/IRQ) of the SC16IS750, or rather the one side of the related pull-up resistor, to the pin header directly to the left side of it. See the enclosed illustration.

Dual-channel UART/GPIO bridge

Derived from the single-channel breakout board, the new development from CJMCU (Changjiang Intelligent Technology Co., Ltd.) [1] and its clones with an SC16IS752 are also supported. These feature a dual-channel UART/GPIO bridge. All this boards coming with a 1.8432MHz crystal. There are no circuit documents for any of the dual-channel breakout boards.

CJMCU-752WCMCU-752

• SC16IS752 Datasheet [12]

Utilization

The shield abstraction of these breakout boards is deliberately kept small. It is purely for evaluating the necessary drivers and Devicetree bindings on known integration platforms. Due to the large number of clones and the associated PCB designations and product names, only two basic shield names are used and extended by the respective short name of the serial peripheral bus to be used. A special case is the suffix _noirq. This is necessary if a faulty single-channel breakout board without interrupt line is to be used. The various connectors on the single and dual channel boards are generally defined using their own Nyxus header bindings:

	I2C shield names	SPI shield names	DTS header bindings
SC16IS750	cjmcu_750_i2c cjmcu_750_i2c_noirq	cjmcu_750_spi cjmcu_750_spi_noirq	cjmcu,75x-hif-header cjmcu,75x-gpio-header
SC16IS752	cjmcu_752_i2c cjmcu_752_i2c_noirq	cjmcu_752_spi cjmcu_752_spi_noirq	cjmcu,75x-hif-header cjmcu,75x-gpio-header

This shields can be used with any development board or shield that provides a Devicetree node with the cjmcu,75x-hif-header property in the compatibility. That is needed for GPIO mapping of the reset and optional interrupt line. Users can rely on the CJMCU-75x Interconnection Shield or create their own interconnection shields with the necessary mappings in them.

Programming

Single-channel UART/GPIO bridge (SC16IS750)Dual-channel UART/GPIO bridge (SC16IS752)

SPII2C

west build -b nucleo_f746zg -p always --shield "x_cjmcu_75x cjmcu_750_spi" -d build/cjmcu_750 bridle/samples/helloshell
west flash -d build/cjmcu_750

Interrupt disabled

west build -b nucleo_f746zg -p always --shield "x_cjmcu_75x cjmcu_750_spi_noirq" -d build/cjmcu_750 bridle/samples/helloshell
west flash -d build/cjmcu_750

References

[1] (1,2,3)

https://web.archive.org/web/20150925195021/http://www.cjmcu.com/

[2]

https://www.lillyelectronicsllc.com/

[3]

https://www.lillyelectronicsllc.com/breakout-board-for-sc16is750-i2c-spi-to-uart-ic

[4] (1,2)

https://www.sparkfun.com/products/retired/9981

[5]

https://www.sparkfun.com/datasheets/BreakoutBoards/SC16IS750_Breakout-v13.pdf

[6]

https://oshwlab.com/rexut95/sparkfun-sc16is750-breakout

[7] (1,2)

https://www.sparkfun.com/products/retired/9745

[8]

https://www.sparkfun.com/datasheets/BreakoutBoards/SC16IS750_Breakout-v12.pdf

[9] (1,2)

https://www.nxp.com/products:SC16IS740_750_760

[10] (1,2,3,4)

https://www.nxp.com/docs/en/data-sheet/SC16IS740_750_760.pdf

[11] (1,2)

https://www.nxp.com/products:SC16IS752_SC16IS762

[12] (1,2)

https://www.nxp.com/docs/en/data-sheet/SC16IS752_SC16IS762.pdf