I am looking at an ST7066U controller for a 2x16 LCD. The datasheet has these assembly instructions that I would like to change to C code.
CHK_BUSY: ;Check Busy Flag
CLR RS
SETB RW
SETB E
JB P1.7,$
CLR E
RET
What does JB P1.7, $ mean?
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3\$\begingroup\$ This type of question is usually answered directly by just looking at the datasheet or assembly language reference for your particular processor. \$\endgroup\$– user4574Nov 30, 2020 at 16:49
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2\$\begingroup\$ High-time you start to learn how to read datasheets. \$\endgroup\$– Mitu RajNov 30, 2020 at 19:03
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2 Answers
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The JB instruction branches to the address specified in the second operand if the value of the bit specified in the first operand is 1. The bit that is tested is not modified. No flags are affected by this instruction.
Source: https://www.keil.com/support/man/docs/is51/is51_jb.htm
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\$\begingroup\$ I read that in the datasheet, I understood that part, if the first operand
P1.7is HIGH, then it shall go to the address in the second operand$, however I didn't understand it in this context, which address does$points to? \$\endgroup\$ Nov 30, 2020 at 23:53 -
\$\begingroup\$ The $ refers to the address of the instruction itself, so the instruction is executed over and over again, until the device is no longer busy. \$\endgroup\$ Jul 20, 2022 at 7:29
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The ST7066U's datasheet has some example code for the 8051 MPU.
From the 8051's instruction set:
Operation: JB Function: Jump if Bit Set Syntax: JB bit addr, reladdr Instructions OpCode Bytes Flags JB bit addr,reladdr 0x20 3 None Description: JB branches to the address indicated by reladdr if the bit indicated by bit addr is set. If the bit is not set program execution continues with the instruction following the JB instruction.
