Programming a ATtiny85 using the serial monitor to debug

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Hi. This is the first time on this site so please forgive any mistakes.
I am trying to program a ATtiny85 on a breadboard and connected to a Arduino Uno and use a serial monitor to debug. Verification is okay, uploading without the TX cable connected is okay but when the TX cable is attached it takes about 1 minute 50 seconds to upload and then I get the following error message :
avrdude: stk500_recv(): programmer is not responding

avrdude: stk500_getsync() attempt 8 of 10: not in sync: resp=0x03

The ATtiny is connected to the Arduino as follows:
Physical pin 1 to Arduino pin 10
pin 3 to pin TX1
pin 4 to ground
pin 5 to pin 11 and a LED
pin 6 to pin 12
pin 7 to pin 13
pin 8 to 5v

The library file is :
#include <SendOnlySoftwareSerial.h>
SendOnlySoftwareSerial Serial(4);

Board info:
BN; Arduino Uno
VID: 2341
PID: 0043
Operating system: Windows 10
IDE version: 1.8.19 (Windows Store 1.8.57.0)
As a newcomer I am not allowed to upload any files unfortunately.

Any help would be greatly appreciated.

Thank you in advance.

Bob May

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Welcome
Take some time to read the sticky post at the top of every section titled: how to get the most out of this forum. It will explain what you need to provide to get good responses and also how to use code tags.

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Your forgot a lot of information. I guess you use the UNO as a programmer and "upload" means actually upload using programmer. Otherwise your description doesn't make sense.

If my guess is correct, the serial interface of the UNO is used for the communication with the PC, talking the stk500 protocol. If the connection between pin 3 (Tiny) and pin 1 (UNO) exists and the old sketch is still running, the TX pin of the UNO is constantly pulled high by the Tiny making a communication impossible.

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