Slow AMBA Peripherals
13-19
GMS30C7201 Data Sheet
When RCVR FIFO and receiver interrupts are enabled, RCVR FIFO time-out interrupts
occurs as follows:
1
A FIFO time-out interrupt occurs if the following conditions exist:
-
at least one character is in the FIFO
-
the most recent serial character received was longer than four continuous
character times ago (if two stop bits are programmed, the second one is
included in this time delay)
-
the most recent CPU read of the FIFO was longer than four continuous
character times ago
This will cause a maximum character received to interrupt issued delay of 160
ms at 300 baud with a 12-bit character.
2
Character times are calculated by using the RCLK input, which is the internal
signal of UART for a clock signal (this makes the delay proportional to the baud
rate).
3
When a time-out interrupt has occurred, it is cleared and the timer is reset
when the CPU reads one character from the RCVR FIFO.
4
When a time-out interrupt has not occurred the time-out timer is reset after a
new character is received or after the CPU reads the RCVR FIFO.
When the XMIT FIFO and transmitter interrupts are enabled (FCR 0 = 1, IER 1 = 1),
XMIT interrupts occurs as follows:
1
The transmitter holding register interrupt (02) occurs when the XMIT FIFO is
empty. It is cleared as soon as the transmitter holding register is written to (1 to
16 characters may be written to the XMIT FIFO while servicing this interrupt)
or the IIR is read.
2
The transmitter FIFO empty indications will be delayed 1 character time minus
the last stop bit time whenever the following occurs: THRE = 1 and there has
not been at least two bytes at the same time in the transmit FIFO since the last
THRE = 1. The first transmitter interrupt affect changing FCR0 will be
immediate if it is enabled.
Character time-out and RCVR FIFO trigger level interrupts have the same priority as
the current received data available interrupt; XMIT FIFO empty has the same priority
as the current transmitter holding register empty interrupt.
Test Registers of Uart
Four extra registers are provided inside the UART for test purposes. They are memory
mapped as shown in
Table 13-11: UART test registers
.
Note
These registers should only be used for test purposes, and should not be accessed
during normal operation.
Detailed descriptions for each of the four registers now follow.
Registers
Read
Write
Width
Base Address + 0x20
UartEN
UartEN
1-bit
Base Address + 0x30
UartTIR
7-bit. Write-only.
Base Address + 0x34
UartTOR
3-bit. Read-only.
Base Address + 0x3C
UartTICCLK
Dummy address for generating TIC
Clock. Write-only.
Table 13-11: UART test registers