XR68C92 datasheet(21/33 Pages) EXAR

21 / 33 page

XR68C92/192

Rev. 1.33

must be disabled and its interrupt must be masked. The

following table shows how to select the clock source for

the C/T when used in counter mode or timer mode:

ACR Bit-7: Baud rate table Select.

This bit is used to select between two sets of baud rate

tables. See Baudrate table on Page 18. It should be

changed only after both channels have been reset and

disabled.

0 = Set 1

1 = Set 2

ISR Bit-1: Receive ready A .

This bit is set when channel A's receive buffer (FIFO) is

filled above the programmed receive trigger level condi-

tion (see MR0A bit-6 and MR1A bit-6). For example, if

a RX trigger level of '6' is chosen, this bit will be set

whenever the RX FIFO contains six or more bytes. This

bit can be cleared by reading the data out of the FIFO

till it falls below the trigger level.

ISR Bit-2: Channel A change in break.

This bit is set when channel A receiver detects the

beginning or the end of a break condition. It is reset

when the CPU issues a channel A reset break change

interrupt command (CRA bits 7-4 = 0x5).

ISR Bit-3: Counter/Timer (C/T) ready.

In counter mode, this bit is set when the C/T reaches

terminal count. In timer mode, this bit is set each time

the C/T output switches from low to high (rising edge -

see Figure 2). In either mode, this bit is cleared by a

stop counter command.

ISR Bit-4: Transmit ready B.

This bit is set when channel B's transmit buffer (FIFO)

is filled below the programmed transmit trigger level

(see MR0B bits 5-4). For example, if a TX trigger level

of '4' is chosen, this bit will be set whenever the TX

FIFO has four or more empty locations. This bit can be

cleared by loading the TX FIFO above the trigger level.

ISR Bit-5: Receive ready B.

This bit is set when channel B's receive buffer (FIFO)

is filled above the programmed receive trigger level

condition (see MR0B bit-6 and MR1B bit-6). For ex-

ample, if a RX trigger level of '6' is chosen, this bit will

be set whenever the RX FIFO contains six or more

bytes. This bit can be cleared by reading the data out

of the FIFO till it falls below the trigger level.

ISR Bit-6. Channel B change in break.

This bit is set when channel B receiver detects the

beginning or the end of a break condition. It is reset

when the CPU issues a channel B reset break change

interrupt command (CRB bits 7-4 = 0x5).

ISR Bit-7. Input port change status.

This bit is set when a change of state has occurred at

the IP0, IP1, IP2, or IP3 inputs, and that event has been

enabled to cause an interrupt by programming ACR

Bits 3-0. This bit is cleared when the CPU reads the

input port change register.

INTERRUPT STATUS REGISTER (ISR)

This register provides the status of all potential interrupt

sources. The contents of this register are logically

“AND”-ed with the contents of the interrupt mask

signal is inverted to produce the -INT output. All active

interrupt sources are visible by reading the ISR, re-

gardless of the contents of the interrupt mask register.

Reading the ISR has no effect on any interrupt source.

Each active interrupt source must be cleared in a

source-specific fashion to clear the ISR. All interrupt

sources are cleared when the XR68C92/192 is reset.4

ISR Bit-0: Transmit ready A.

This bit is set when channel A's transmit buffer (FIFO)

is filled below the programmed transmit trigger level

(see MR0A bits 5-4). For example, if a TX trigger level

of '4' is chosen, this bit will be set whenever the TX

FIFO has four or more empty locations. This bit can be

cleared by loading the TX FIFO above the trigger level.

ACR

C/T

Clock Source

Bits 6:4

Mode

0 0 0

Counter

External (IP2)

0 0 1

Counter

TXAClk1-Transmit A 1X clock

0 1 0

Counter

TXBClk1-Transmit B 1X clock

0 1 1

Counter

Crystal or External Clock

(XTAL1/Clk) Divided by 16

1 0 0

Timer

External (IP2)

1 0 1

Timer

External (IP2) Divided by 16

1 1 0

Timer

Crystal or External Clock

(XTAL1/Clk)

1 1 1

Timer

Crystal or External Clock

(XTAL1/Clk) Divided by 16

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