
Slow AMBA Peripherals
13-15
GMS30C7201 Data Sheet
Bit 6:
This bit is the Transmitter Empty (TEMT) indicator. Bit 6 is set to a logic
1 whenever the Transmitter Holding Register (THR) and the
Transmitter Shift Register (TSR) are both empty. It is reset to a logic 0
whenever either the THR or TSR contains a data character. In the
FIFO mode this bit is set to one whenever the transmitter FIFO and
register are both empty.
In the 16450 mode this is a 0. In the FIFO mode LSR7 is set when
there is at least one parity error, framing error or break indication in the
FIFO. LSR7 is cleared when the CPU reads the LSR, if there are no
subsequent errors in the FIFO.
The Line Status Register is intended for read operations only.
Bit 7:
Note
FIFO Control Register
This is a write-only register at the same location as the IIR (the IIR is a read-only
register). This register is used to enable the FIFOs, clear the FIFOs and set the RCVR
FIFO trigger level.
Bit 0:
Writing a 1 to FCR0 enables both the XMIT and RCVR FIFOs.
Resetting FCR0 will clear all bytes in both FIFOs. When changing from
FIFO Mode to 16C450 Mode and vice versa, data is automatically
cleared from the FIFOs. This bit must be a 1 when other FCR bits are
written to or they will not be programmed.
Bit 1:
Writing a 1 to FCR1 resets its counter logic to 0. The shift register is
not cleared. The 1 that is written to this bit position is self-clearing.
Bit 2:
Writing a 1 to FCR2 resets its counter logic to 0. The shift register is
not cleared. The 1 that is written to this bit position is self-clearing.
Bit 3:
FCR3 is not used.
Bit 4, 5:
FCR4 to FCR5 are reserved for future use.
Bit 6, 7:
FCR6 and FCR7 are used to set the trigger level for the RCVR FIFO
interrupt.
Interrupt Identification Register
In order to provide minimum software overhead during data character transfers, the
UART prioritizes interrupts into four levels and records these in the Interrupt
Identification Register. The four levels of interrupt conditions are, in order of priority:
Receiver Line Status
Received Data Ready
Transmitter Holding Register Empty
MODEM Status.
FCR[7:6]
RCVR FIFO
Trigger Level (Bytes)
00
01 (default)
01
04
10
08
11
14
Table 13-9: RCVR FIFO interrupt