NXP Semiconductors

SC18IM704

7 Functional description

of a full-functional advanced UART. The UART communicates with the host through the

TX and RX pins. The serial data format is fixed: one start bit, 8 data bits, and one stop

bit. After reset the baud rate defaults to 9600 bit/s, and can be changed through the Baud

Rate Generator (BRG) registers.

After a power-up sequence or a hardware reset, SC18IM704 will send two continuous

bytes to the host to indicate a start-up condition. These two bytes are 0x4F and 0x4B;

‘OK’ in ASCII.

7.1 UART message format

internal registers through a series of ASCII commands. Table 4 lists the ASCII

commands supported by SC18IM704, and also their hexadecimal value representation.

Unrecognized commands are ignored by the device.

To prevent the host from handing SC18IM704 due to an unfinished command sequence,

SC18IM704 has a time-out feature. The delay between any two bytes of data coming

from the host should be less than 655 ms. If this condition is not met, SC18IM704

will time-out and clear the receive buffer. SC18IM704 then starts to wait for the next

command from the host.

ASCII command

Hex value

Command function

S

0x53

P

0x50

R

0x52

read SC18IM704 internal register

W

0x57

write to SC18IM704 internal register

I

0x49

read GPIO port

O

0x4F

write to GPIO port

Z

0x5A

power down

Table 4. ASCII commands supported by SC18IM704

7.1.1 Write N bytes to target device

begins with the first byte (DATA 0) and ends with the last byte (DATA N). The frame is

then terminated with a P character. Once the host issues this command, SC18IM704 will

002aac048

NUMBER

OF BYTES

S CHAR. TARGET ADR.

+ W

host sends

DATA 0

DATA N

P CHAR.

Figure 3. Write N bytes to target device

SC18IM704

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© NXP B.V. 2021. All rights reserved.

Product data sheet

Rev. 1.0 — 22 September 2021

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