Any difference between UART STAT and INTSTAT when reading interrupt flags??

[jdupre]

The UARTS in the LPC15xx have both a STAT and an INTSTAT register.

Is there any difference in reading a UART's STAT register vs. INTSTAT?

Put another way, if an interrupt flag bit is set in INTSTAT will it always be set in STAT also?

Is there any reason to use INTSTAT instead of STAT in an ISR?  (Understanding that INTSTAT is read only and may include bits that are not interrupt flags.)

[soledad]

Hi Joseph,

It is  only for simplify software.

The STAT register primarily provides a complete set of USART status flags for software to read. Flags other than read-only flags may be cleared by writing ones to corresponding bits of STAT. Interrupt status flags that are read-only and cannot be cleared by software, can be masked using the INTENCLR register.

The error flags for received noise, parity error, framing error, and overrun are set immediately upon detection and remain set until cleared by software action in STAT.

Table. USART registerName = STAT addressOffset = 0x008

Bit	Symbol	Description	Reset value	Access
0	RXRDY	Receiver Ready flag. When 1, indicates that data is available to be read from the receiver buffer. Cleared after a read of the RXDAT or RXDATSTAT registers.	0	RO
1	RXIDLE	Receiver Idle. When 0, indicates that the receiver is currently in the process of receiving data. When 1, indicates that the receiver is not currently in the process of receiving data.	1	RO
2	TXRDY	Transmitter Ready flag. When 1, this bit indicates that data may be written to the transmit buffer. Previous data may still be in the process of being transmitted. Cleared when data is written to TXDAT. Set when the data is moved from the transmit buffer to the transmit shift register.	1	RO
3	TXIDLE	Transmitter Idle. When 0, indicates that the transmitter is currently in the process of sending data.When 1, indicate that the transmitter is not currently in the process of sending data.	1	RO
4	CTS	This bit reflects the current state of the CTS signal, regardless of the setting of the CTSEN bit in the CFG register. This will be the value of the CTS input pin unless loopback mode is enabled.	NA	RO
5	DELTACTS	This bit is set when a change in the state is detected for the CTS flag above. This bit is cleared by software.	0	W1
6	TXDISINT	Transmitter Disabled Interrupt flag. When 1, this bit indicates that the USART transmitter is fully idle after being disabled via the TXDIS in the CFG register (TXDIS = 1).	0	RO
7	-	Reserved. Read value is undefined, only zero should be written.	NA	NA
8	OVERRUNINT	Overrun Error interrupt flag. This flag is set when a new character is received while the receiver buffer is still in use. If this occurs, the newly received character in the shift register is lost.	0	W1
9	-	Reserved. Read value is undefined, only zero should be written.	NA	NA
10	RXBRK	Received Break. This bit reflects the current state of the receiver break detection logic. It is set when the Un_RXD pin remains low for 16 bit times. Note that FRAMERRINT will also be set when this condition occurs because the stop bit(s) for the character would be missing. RXBRK is cleared when the Un_RXD pin goes high.	0	RO
11	DELTARXBRK	This bit is set when a change in the state of receiver break detection occurs. Cleared by software.	0	W1
12	START	This bit is set when a start is detected on the receiver input. Its purpose is primarily to allow wake-up from Deep-sleep or Power-down mode immediately when a start is detected. Cleared by software.	0	W1
13	FRAMERRINT	Framing Error interrupt flag. This flag is set when a character is received with a missing stop bit at the expected location. This could be an indication of a baud rate or configuration mismatch with the transmitting source.	0	W1
14	PARITYERRINT	Parity Error interrupt flag. This flag is set when a parity error is detected in a received character..	0	W1
15	RXNOISEINT	Received Noise interrupt flag. Three samples of received data are taken in order to determine the value of each received data bit, except in synchronous mode. This acts as a noise filter if one sample disagrees. This flag is set when a received data bit contains one disagreeing sample. This could indicate line noise, a baud rate or character format mismatch, or loss of synchronization during data reception.	0	W1
31:16	-	Reserved. Read value is undefined, only zero should be written.	NA	NA

Note: RO = Read-only, W1 = write 1 to clear.

The read-only INTSTAT register provides a view of those interrupt flags that are currently enabled. This can simplify software handling of interrupts.

Table. USART registerName = INTSTAT addressOffset = 0x024

Bit	Symbol	Description	Reset Value
0	RXRDY	Receiver Ready flag.	0
1	-	Reserved. Read value is undefined, only zero should be written.	NA
2	TXRDY	Transmitter Ready flag.	1
4:3	-	Reserved. Read value is undefined, only zero should be written.	NA
5	DELTACTS	This bit is set when a change in the state of the CTS input is detected.	0
6	TXDISINT	Transmitter Disabled Interrupt flag.	0
7	-	Reserved. Read value is undefined, only zero should be written.	NA
8	OVERRUNINT	Overrun Error interrupt flag.	0
10:9	-	Reserved. Read value is undefined, only zero should be written.	NA
11	DELTARXBRK	This bit is set when a change in the state of receiver break detection occurs.	0
12	START	This bit is set when a start is detected on the receiver input.	0
13	FRAMERRINT	Framing Error interrupt flag.	0
14	PARITYERRINT	Parity Error interrupt flag.	0
15	RXNOISEINT	Received Noise interrupt flag.	0
31:16	-	Reserved. Read value is undefined, only zero should be written.	NA

Have a great day,
Sol

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[alikarakaş]

you say in datasheet :

TXRDY

Transmitter Ready flag. When 1, this bit indicates that data may be written to the transmit buffer. Previous data may still be in the process of being transmitted. Cleared when data is written to TXDAT. Set when the data is moved from the transmit buffer to the transmit shift register.

But how can i set in main loop im using this code like this :

while((Chip_UARTN_GetStatus(LPC_USART1) & UARTN_STAT_TXRDY) != 0)
{ LPC_USART1->TXDATA = (uint32_t) 0x10|0x100; }
_delay_ms(10);
while((Chip_UARTN_GetStatus(LPC_USART1) & UARTN_STAT_TXRDY) != 0)
{ LPC_USART1->TXDATA = (uint32_t) 0x01&~0x100; }

 for 9 bit transmission. İf i cant write delay function code is passed