# Writing to a serial port using SerialPorts.jl
**URL:** https://discourse.julialang.org/t/writing-to-a-serial-port-using-serialports-jl/84236
**Category:** New to Julia
**Tags:** question
**Created:** [July 14, 2022, 6:42pm UTC](https://discourse.julialang.org/t/writing-to-a-serial-port-using-serialports-jl/84236 "2022-07-14T18:42:12Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@Aditya\_Rai](https://discourse.julialang.org/u/Aditya_Rai)
#### Post date: [July 14, 2022, 6:42pm UTC](https://discourse.julialang.org/t/writing-to-a-serial-port-using-serialports-jl/84236/1 "2022-07-14T18:42:12Z")
Hello Everyone,
I was trying to write to a device (laser) using SerialPorts.jl however there seems to be some error in my code as the device does not respond to my commands.
I was able to wrtie to this device using MATLAB. I have attached an image of both MATLAB and Julia code for your reference.
MATLAB Code:
```julia
laser = serial('COM6','BaudRate',9600,'DataBits',8,'Parity','none','FlowControl','none','StopBits',1);
fopen(laser);
fwrite(laser, [126 1 1 1 1]);
pause(1/2) % set CW mode
fclose(laser);
pause(1/2);
```
Julia Code:
```julia
using SerialPorts
laser_port = "COM6"
laser_baudrate=9600
ser = SerialPort(laser_port, laser_baudrate)
print("The port is available \n")
write(ser, [126 1 1 1 1])
close(ser)
```
I am a complete beginner in interfacing with serial ports, any help in understanding why passing the command ( [126 1 1 1 1] ) works in MATLAB but doesn’t in Julia.
Any help would be appreciated. Thanks.
Edit: I would also like to mention I am using the RS232 communication protocol to communicate with the laser device.
---
### Author:  [@jebej](https://discourse.julialang.org/u/jebej)
#### Post date: [July 14, 2022, 7:03pm UTC](https://discourse.julialang.org/t/writing-to-a-serial-port-using-serialports-jl/84236/2 "2022-07-14T19:03:51Z")
Try sending an actual byte array with `write(ser, UInt8[126 1 1 1 1])` instead.
---
### Author:  [@Aditya\_Rai](https://discourse.julialang.org/u/Aditya_Rai)
#### Post date: [July 14, 2022, 7:06pm UTC](https://discourse.julialang.org/t/writing-to-a-serial-port-using-serialports-jl/84236/3 "2022-07-14T19:06:55Z")
Thanks for the quick response @jebej.
Would you mind explaining, what’s the difference between sending the data as byte array using UInt8 and sending the array as it is?
---
### Author:  [@jebej](https://discourse.julialang.org/u/jebej)
#### Post date: [July 14, 2022, 7:16pm UTC](https://discourse.julialang.org/t/writing-to-a-serial-port-using-serialports-jl/84236/4 "2022-07-14T19:16:02Z")
The actual bytes you are sending differ. With `[126 1 1 1 1]`, you are sending 5 64bit integers, whereas with `UInt8[126 1 1 1 1]` it’s 5 8bit integers. You can see the difference by “casting” the `Int64` array to `UInt8`:
```julia
julia> reinterpret(UInt8, [126, 1, 1, 1, 1])
40-element reinterpret(UInt8, ::Vector{Int64}):
0x7e
0x00
⋮
0x00
0x00
```
The vector of 5 64bit integers is equivalent to 40 bytes of data.
In Julia, types are more strict than in MATLAB and if you tell the function to write `UInt64`, it will do just that. MATLAB does this implicit conversion for you which is probably not super ideal, even if it might work in most cases.
Note that I would also recommend using 1D arrays, that is with commas: `UInt8[126,1,1,1,1]`.
---
### Author:  [@Aditya\_Rai](https://discourse.julialang.org/u/Aditya_Rai)
#### Post date: [July 14, 2022, 7:47pm UTC](https://discourse.julialang.org/t/writing-to-a-serial-port-using-serialports-jl/84236/5 "2022-07-14T19:47:36Z")
Thanks for that comprehensive answer, I was able to understand the difference!