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IO-Jack — UART Mode

IO jack in UART mode — serial interface with configuration via cfg and data transfer via uart.

How It Works

In UART mode, an IO jack operates as a serial interface with two subtopics:

Subtopic Purpose
port Set UART settings over
uart Send / receive raw UART data bytes

Configuration (port)

The interface is configured with five parameters before data transfer. Short form: Baudrate-Databits-Parity-Stopbits (N = none, E = even, O = odd):

Configuration Baud rate Data bits Parity Stop bits RS485
Standard · 115200-8-N-1 115,200 8 none 1 off
Classic · 9600-8-N-1 9,600 8 none 1 off
7-bit, even · 9600-7-E-1 9,600 7 even 1 off
RS485 bus · 500000-8-N-1 500,000 8 none 1 on
High speed · 3000000-8-N-1 3,000,000 8 none 1 off

Parameters

Baud Rate

Baud rate (bit/s) Constant Code
300 UartBaud300 0x00
600 UartBaud600 0x01
1,200 UartBaud1200 0x02
2,400 UartBaud2400 0x03
4,800 UartBaud4800 0x04
9,600 UartBaud9600 0x05
19,200 UartBaud19200 0x06
38,400 UartBaud38400 0x07
115,200 UartBaud115200 0x08
230,400 UartBaud230400 0x09
500,000 UartBaud500000 0x0A
1,000,000 UartBaud1000000 0x0B
3,000,000 UartBaud3000000 0x0C
5,000,000 UartBaud5000000 0x0D

Data Bits

Data bits Constant Value
7 UartData7 0x2000
8 UartData8 0x0000
9 UartData9 0x1000

Parity

Parity Constant Value
none UartParityNone 0x0000
even UartParityEven 0x0400
odd UartParityOdd 0x0800

Stop Bits

Stop bits Constant Value
1 UartStopbits1 0x0000
1.5 UartStopbits15 0x0100
2 UartStopbits2 0x0200

RS485

RS485 Constant
off (default)
on UartRS485

Uart Rx

RS485 Constant
on (default)
off Uart Receive off

16-Bit Configuration Word

The configuration is transmitted via cfg with the Config UART command (code 25, available in the 16-bit frame only). The payload is one 16-bit word — assembled by bitwise OR of the field values:

Bits Field Values
15 Uart RX off 0x8000 · on 0x0000
14 RS485 off 0x0000 · on 0x4000
12–13 Data bits 8 0x0000 · 9 0x1000 · 7 0x2000
10–11 Parity none 0x0000 · even 0x0400 · odd 0x0c00
7–8 Stop bits 1 0x0000 · 1.5 0x0100 · 2 0x0200
0–7 Baud rate code from the table above

Examples:

Configuration = Config word
115200-8-N-1 0x0008
9600-8-N-1 0x0005
9600-7-E-1 0x2405
500000-8-N-1 (RS485) 0x800A
3000000-8-N-1 0x000C

Transmission: 4 Bytes for 16 Bit of Data

Config UART is transmitted with code 25 in the 16-bit frame. This frame is 4 bytes long, even though the command code (6 bit) and config word (16 bit) together amount to only 22 bits of payload — the rest are fixed marker bits that make the frame self-synchronizing: every byte starts with either 1110 (lead byte, once) or 10 (continuation byte, 3×).

Byte 0:  1 1 1 0  │ C5 C4 C3 C2
Byte 1:  1 0      │ C1 C0 D15 D14 D13 D12
Byte 2:  1 0      │ D11 D10 D9 D8 D7 D6
Byte 3:  1 0      │ D5 D4 D3 D2 D1 D0
  • C5…C0 = command code (6 bit) → here 25 = 011001
  • D15…D0 = config word (16 bit) → e.g. 0x0008 = 0000 0000 0000 1000

Building It via Shift & Mask

Instead of bit by bit, each byte can be computed directly from Code and Word using shift (>>) and mask (&):

Byte0 = 0xE0 | (Code >> 2)                    // Lead byte:      1110 + upper 4 bits of the code
Byte1 = 0x80 | ((Code & 0x03) << 4)           // Continuation 1: lower 2 bits of the code
             | (Word >> 12)                  //               + upper 4 bits of the data (15–12)
Byte2 = 0x80 | ((Word >> 6) & 0x3F)           // Continuation 2: middle 6 bits of the data (11–6)
Byte3 = 0x80 | (Word & 0x3F)                  // Continuation 3: lower 6 bits of the data (5–0)
  • 0xE0 = 1110 0000 → lead byte marker
  • 0x80 = 1000 0000 → continuation byte marker
  • 0x03 = masks the lower 2 bits (remainder of the code)
  • 0x3F = masks the lower 6 bits (one data chunk)

Applied to 115200-8-N-1 (Code = 25, Word = 0x0008):

Byte0 = 0xE0 | (25 >> 2)                       = 0xE0 | 0x06        = 0xE6
Byte1 = 0x80 | ((25 & 0x03) << 4) | (0x0008 >> 12)
      = 0x80 | (1 << 4)           | 0x00       = 0x80 | 0x10 | 0x00 = 0x90
Byte2 = 0x80 | ((0x0008 >> 6) & 0x3F)           = 0x80 | 0x00        = 0x80
Byte3 = 0x80 | (0x0008 & 0x3F)                  = 0x80 | 0x08        = 0x88

→ Complete frame: E6 90 80 88

The receiver reverses the formulas: Code = ((Byte0 & 0x0F) << 2) | ((Byte1 >> 4) & 0x03), Word = ((Byte1 & 0x0F) << 12) | ((Byte2 & 0x3F) << 6) | (Byte3 & 0x3F). From Code = 25 (Config UART) and Word = 0x0008, the baud rate/data bits/parity/stop bits tables above can then be applied in reverse.

Cross References