USART not working

[sue]

Posted on August 16, 2010 at 02:07

USART not working

[sue]

Posted on May 17, 2011 at 14:02

Hi Clive, thanks again for your help.

I have set the USART prescaler to 1 RCC_CFGR is zeroed and that is why receive is now working. But send is not.  Can you offer any other suggestions re send?

[Tesla DeLorean]

Posted on May 17, 2011 at 14:02

>>Looking at your original post, you do not appear to enable the clock for USART1.

Using USART2 this would not appear to be a problem.

[Tesla DeLorean]

Posted on May 17, 2011 at 14:02

Hard to say, make sure you are enabling receive/transmit modes of all the USARTs

[John F.]

Posted on May 17, 2011 at 14:02

Looking at your original post, you do not appear to enable the clock for USART1. You really ought to learn C. It's not difficult!

[John F.]

Posted on May 17, 2011 at 14:02

I'm not sure any of us know what she's doing. I was going by, ''for all three usarts the receive is working (using usart2) (yeehaaa) but send is not (using usart1).  Is there anything different I have to do for send?'' (above).

[Tesla DeLorean]

Posted on May 17, 2011 at 14:02

The following should be a relatively minimal initiation of

USART1,2,3 at 9600 baud from the STM32 reset state. ;***************************************************************************** ; USART1 PA.9  TX, PA.10 RX ; USART2 PA.2  TX, PA.3  RX ; USART3 PB.10 TX, PB.11 RX ;***************************************************************************** InitSystem    PROC         ; Enter from reset routine, STM32 in initial state, clocking from HSI at 8 MHz         ldr    r0, =0x40021000    ; RCC         ldr    r1, =0x0000400C    ; USART1EN | IOPBEN (GPIOB) | IOPAEN (GPIOA)         str    r1, [r0, #24]    ; +24 RCC_APB2ENR         ldr    r1, =0x00060000    ; USART3EN | USART2EN         str    r1, [r0, #28]    ; +28 RCC_APB1ENR         ldr    r0, =0x40010800    ; GPIOA         ldr    r1, =0x444444B4    ; PA.9 USART1_TX 50MHz AF_PP         str    r1, [r0, #4]    ; +4  GPIOx_CRH         ldr    r1, =0x44444B44    ; PA.2 USART2_TX 50MHz AF_PP         str    r1, [r0, #0]    ; +0  GPIOx_CRL         ldr    r0, =0x40010C00    ; GPIOB         ldr    r1, =0x44444B44    ; PB.10 USART3_TX 50MHz AF_PP         str    r1, [r0, #4]    ; +4  GPIOx_CRH         ldr    r0, =0x40013800    ; UART1         bl    InitUART         ldr    r0, =0x40004400    ; UART2         bl    InitUART         ldr    r0, =0x40004800    ; UART3         bl    InitUART         bx    lr         ENDP ;***************************************************************************** InitUART    PROC         ; R0 is base address of USART         movs    r1, #0         strh    r1, [r0, #4]    ;  +4 USART_DR         movs    r1, #833    ; 8MHz / 833 == 9600         strh    r1, [r0, #8]    ;  +8 USART_BR         movs    r1, #0x0600         strh    r1, [r0, #16]    ; +16 USART_CR2 = 0x600         movs    r1, #0         strh    r1, [r0, #16]    ; +16 USART_CR2 = 0         movs    r1, #0         strh    r1, [r0, #24]    ; +24 USART_GTPR = 0 - Prescaler         movw    r1, #0x200C    ; 8-bit, no parity, enable TX,TX         strh    r1, [r0, #12]    ; +12 USART_CR1         ldr    r2, =10        ; 10 Pounds iu1        ldr.w    r1, [r0, #0]    ; +0  USART->SR         ands    r1, #0x80    ; TXE         beq    iu1         mov    r1, #'#'         str.w    r1, [r0, #4]    ; +4  USART->DR         subs.w    r2, r2,    #1    ; r2--         bne.n    iu1         bx    lr         ENDP ;*****************************************************************************

[sue]

Posted on May 17, 2011 at 14:02

Hi John, thanks for your post.

In my original post, I was not using USART1, only USART2, and only trying to receive. Having got receive working I am now trying to get send to work, and am using USART1 for that, although I have now added code to use USART2 alternatively.  Of course I have added code to enable everything that has to be enabled for USART1 and USART2 in order to send but I'm not going to post it unless invited to do so as it is now quite large. No point in learning C as we cannot use it in production, it has to be assembler.

[Tesla DeLorean]

Posted on May 17, 2011 at 14:02

There are different prescalers, the fast ones in the RCC unit reset to DIV-BY-1 the internal system and bus clocks.

There is *another* unrelated prescaler in the USART, it relates to the Guard Time for the Smartcard mode, we are NOT using that. It should zero at reset, I simply have code that gets it too that state. Probably overkill. The CR2 stuff is derived from some other ST code, and toggles the sync-clock bits, again probably overkill. Once you get the code working as you want you could probably prune it back.

[sue]

Posted on May 17, 2011 at 14:02

Hi Clive, thanks again for taking the trouble to post.

I am sure everyone, including me, is heartily sick of this topic. I have only the following questions, Clive, about the assembler code you just posted (after that I'll leave you all alone): 1. why do you set USART_CR2 to 0x600 and then immediately clear it to zero? 2. why are you setting the prescalers to zero when in your earlier post you said they have to be set to 1? (and indeed I can see in the reference manual that this is what they have to be set to) 

[Tesla DeLorean]

Posted on May 17, 2011 at 14:02

>>No point in learning C as we cannot use it in production, it has to be assembler.

Some kind of defence/automotive/medical type thing, or you just work with luddites?