GM82C803CN Datasheet, PDF (65/84 Pages) List of Unclassifed Manufacturers – 2.88 MB FDC/ Dual UARTs with FIFO/PIO(EPP/ ECP)/ IDE Interface/ S-IR/ PnP

GM82C803CN
3) When a timeout interrupt has occurred, it is cleared and the timer is reset when the CPU reads one character from
the RCVR FIFO.
4) When a timeout interrupt has not occurred the timeout 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 FCR 0 will be immediate if it is enabled.
Character timeout 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.
FIFO Polled Mode Operation
When FCR 0 = 1 resetting, IER 0, IER 1, IER 2, IER3 or all to zero puts the UART in the FIFO Polled Mode. Since
the RCVR and XMITTER are controlled separately, either one or both can be in the polled mode.
Programmable Baud Generator
The UART contains a programmable Baud Generator. The output frequency of the Baud Rate Generator is 16 the
Baud [divisor # = (frequency input ) (baud rate 16)]. Two 8-bit latches store the divisor in a 16-bit binary
format. These Divisor Latches must be located during initialization to ensure proper operation of the Baud Rate
Generator. Upon loading either of the Divisor Latches, a 16-bit Baud counter is immediately loaded.
Table 4-20. shows decimal divisors for baud rates. For baud rates of 38,400 and below, the minimal error is obtained.
Using a divisor of zero is not recommended.