UART Library
UART hardware module is available with a number of PIC MCUs. mikroBasic PRO for PIC UART Library provides comfortable work with the Asynchronous (full duplex) mode.
You can easily communicate with other devices via RS-232 protocol (for example with PC, see the figure at the end of the topic – RS-232 HW connection). You need a PIC MCU with hardware integrated UART, for example 16F887. Then, simply use the functions listed below.

- UART library routines require you to specify the module you want to use. To select the desired UART module, simply change the letter 1 in the routine prototype for a number from 1 to 2.
- Switching between the UART modules in the UART library is done by the UART_Set_Active function (UART modules have to be previously initialized).
- Number of UART modules per MCU differs from chip to chip. Please, read the appropriate datasheet before utilizing this library.
Library Routines
- UARTx_Init
- UARTx_Data_Ready
- UARTx_Tx_Idle
- UARTx_Read
- UARTx_Read_Text
- UARTx_Write
- UARTx_Write_Text
- UART_Set_Active
Generic Routines
UARTx_Init
Prototype |
sub procedure UARTx_Init(const baud_rate as longint) |
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Returns |
Nothing. |
Description |
Configures and initializes the UART module. The internal UART module module is set to:
Parameters :
Refer to the device data sheet for baud rates allowed for specific Fosc. |
Requires |
You'll need PIC MCU with hardware UART.
![]() Therefore, compiler needs to know the value of the parameter in the compile time. That is why this parameter needs to be a constant, and not a variable. |
Example |
This will initialize hardware UART1 module and establish the communication at 2400 bps: 'This will initialize hardware UART1 module and establish the communication at 2400 bps UART1_Init(2400) |
UARTx_Data_Ready
Prototype |
sub function UARTx_Data_Ready() as byte |
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Returns |
Function returns 1 if data is ready or 0 if there is no data. |
Description |
The function tests if data in receive buffer is ready for reading. |
Requires |
MCU with the UART module. The UART module must be initialized before using this routine. See the UARTx_Init routine. |
Example |
dim receive as byte ... ' read data if ready if (UART1_Data_Ready() = 1) then receive = UART1_Read() end if |
UARTx_Tx_Idle
Prototype |
sub function UARTx_Tx_Idle() as byte |
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Returns |
|
Description |
Use the function to test if the transmit shift register is empty or not. |
Requires |
UART HW module must be initialized and communication established before using this function. See UARTx_Init. |
Example |
' If the previous data has been shifted out, send next data: if (UART1_Tx_Idle = 1) then UART1_Write(_data) end if |
UARTx_Read
Prototype |
sub function UARTx_Read() as byte |
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Returns |
Received byte. |
Description |
The function receives a byte via UART. Use the UARTx_Data_Ready function to test if data is ready first. |
Requires |
MCU with the UART module. The UART module must be initialized before using this routine. See UARTx_Init routine. |
Example |
dim receive as byte ... ' read data if ready if (UART1_Data_Ready() = 1) then receive = UART1_Read() |
UARTx_Read_Text
Prototype |
sub procedure UARTx_Read_Text(dim byref Output as string[255], dim byref Delimiter as string[10], dim Attempts as byte) |
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Returns |
Nothing. |
Description |
Reads characters received via UART until the delimiter sequence is detected. The read sequence is stored in the parameter This is a blocking call: the delimiter sequence is expected, otherwise the procedure exits( if the delimiter is not found). Parameter |
Requires |
UART HW module must be initialized and communication established before using this function. See UARTx_Init. |
Example |
Read text until the sequence “OK” is received, and send back what’s been received: UART1_Init(4800) ' initialize UART module Delay_ms(100) while TRUE if (UART1_Data_Ready() = 1) ' if data is received UART1_Read_Text(output, 'OK', 10) ' reads text until 'OK' is found UART1_Write_Text(output) ' sends back text end if wend. |
UARTx_Write
Prototype |
sub procedure UARTx_Write(dim TxData as byte) |
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Returns |
Nothing. |
Description |
The function transmits a byte via the UART module. Parameters :
|
Requires |
MCU with the UART module. The UART module must be initialized before using this routine. See UARTx_Init routine. |
Example |
dim data_ as byte ... data_ = 0x1E UART1_Write(data_) |
UARTx_Write_Text
Prototype |
sub procedure UARTx_Write_Text(dim byref uart_text as string[255]) |
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Returns |
Nothing. |
Description |
Sends text (parameter |
Requires |
UART HW module must be initialized and communication established before using this function. See UARTx_Init. |
Example |
Read text until the sequence “OK” is received, and send back what’s been received: UART1_Init(4800) ' initialize UART module Delay_ms(100) while TRUE if (UART1_Data_Ready() = 1) ' if data is received UART1_Read_Text(output, 'OK', 10) ' reads text until 'OK' is found UART1_Write_Text(output) ' sends back text end if wend. |
UART_Set_Active
Prototype |
sub procedure UART_Set_Active (dim read_ptr as ^Tread_ptr, dim write_ptr as ^Twrite_ptr, dim ready_ptr as ^Tready_ptr, dim tx_idle_ptr as ^Ttx_idle_ptr) |
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Returns |
Nothing. |
Description |
Sets active UART module which will be used by the UART library routines. Parameters :
|
Requires |
Routine is available only for MCUs with two UART modules. Used UART module must be initialized before using this routine. See UARTx_Init routine |
Example |
UART1_Init(9600); // initialize UART1 module UART2_Init(9600); // initialize UART2 module RS485Master_Init(); // initialize MCU as Master UART_Set_Active(@UART1_Read, @UART1_Write, @UART1_Data_Ready, @UART1_Tx_Idle); // set UART1 active RS485Master_Send(dat,1,160); // send message through UART1 UART_Set_Active(@UART2_Read, @UART2_Write, @UART2_Data_Ready, @UART2_Tx_Idle); // set UART2 active RS485Master_Send(dat,1,160); // send through UART2 |
UART_Data_Ready
Prototype |
sub function UART_Data_Ready() as byte |
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Returns |
Function returns 1 if data is ready or 0 if there is no data. |
Description |
The function tests if data in receive buffer is ready for reading. This is a generic routine which uses the active UART module previously activated by the UART_Set_Active routine. |
Requires |
MCU with the UART module. The UART module must be initialized before using this routine. See the UARTx_Init routine. |
Example |
dim receive as byte ... ' read data if ready if (UART1_Data_Ready() = 1) then receive = UART1_Read() end if |
UART_Tx_Idle
Prototype |
sub function UART_Tx_Idle() as byte |
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Returns |
|
Description |
Use the function to test if the transmit shift register is empty or not. This is a generic routine which uses the active UART module previously activated by the UART_Set_Active routine. |
Requires |
UART HW module must be initialized and communication established before using this function. See UARTx_Init. |
Example |
' If the previous data has been shifted out, send next data: if (UART1_Tx_Idle = 1) then UART1_Write(_data) end if |
UART_Read
Prototype |
sub function UART_Read() as byte |
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Returns |
Received byte. |
Description |
The function receives a byte via UART. Use the UART_Data_Ready function to test if data is ready first. This is a generic routine which uses the active UART module previously activated by the UART_Set_Active routine. |
Requires |
MCU with the UART module. The UART module must be initialized before using this routine. See UARTx_Init routine. |
Example |
dim receive as byte ... ' read data if ready if (UART1_Data_Ready() = 1) then receive = UART1_Read() |
UART_Read_Text
Prototype |
sub procedure UART_Read_Text(dim byref Output as string[255], dim byref Delimiter as string[10], dim Attempts as byte) |
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Returns |
Nothing. |
Description |
Reads characters received via UART until the delimiter sequence is detected. The read sequence is stored in the parameter This is a blocking call: the delimiter sequence is expected, otherwise the procedure exits( if the delimiter is not found). Parameter This is a generic routine which uses the active UART module previously activated by the UART_Set_Active routine. |
Requires |
UART HW module must be initialized and communication established before using this function. See UARTx_Init. |
Example |
Read text until the sequence “OK” is received, and send back what’s been received: UART1_Init(4800) ' initialize UART module Delay_ms(100) while TRUE if (UART1_Data_Ready() = 1) ' if data is received UART1_Read_Text(output, 'OK', 10) ' reads text until 'OK' is found UART1_Write_Text(output) ' sends back text end if wend. |
UART_Write
Prototype |
sub procedure UART_Write(dim TxData as byte) |
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Returns |
Nothing. |
Description |
The function transmits a byte via the UART module. This is a generic routine which uses the active UART module previously activated by the UART_Set_Active routine. Parameters :
|
Requires |
MCU with the UART module. The UART module must be initialized before using this routine. See UARTx_Init routine. |
Example |
dim data_ as byte ... data_ = 0x1E UART1_Write(data_) |
UART_Write_Text
Prototype |
sub procedure UART_Write_Text(dim byref uart_text as string[255]) |
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Returns |
Nothing. |
Description |
Sends text (parameter This is a generic routine which uses the active UART module previously activated by the UART_Set_Active routine. |
Requires |
UART HW module must be initialized and communication established before using this function. See UARTx_Init. |
Example |
Read text until the sequence “OK” is received, and send back what’s been received: UART1_Init(4800) ' initialize UART module Delay_ms(100) while TRUE if (UART1_Data_Ready() = 1) ' if data is received UART1_Read_Text(output, 'OK', 10) ' reads text until 'OK' is found UART1_Write_Text(output) ' sends back text end if wend. |
Library Example
This example demonstrates simple data exchange via UART. If MCU is connected to the PC, you can test the example from the mikroBasic PRO for PIC USART Terminal.
program UART dim uart_rd as byte main: UART1_Init(9600) ' Initialize UART module at 9600 bps Delay_ms(100) ' Wait for UART module to stabilize UART1_Write_Text("Ready") UART1_Write(10) ' Line Feed UART1_Write(13) ' Carriage Return while (TRUE) ' Endless loop if (UART1_Data_Ready() <> 0) then ' If data is received, uart_rd = UART1_Read() ' read the received data, UART1_Write(uart_rd) ' and send data via UART end if wend end.
HW Connection
UART HW connection
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