Philips Semiconductors

Product specification

SC26C94

Quad universal asynchronous receiver/transmitter (QUART)

1995 May 1

20

I/O Port Control Channel B (IOPCRB)

IOPCR[xx]

Pin Control Bits

IOPCRb[7:6]

IOPCRb[5:4]

IOPCRb[3:2]

IOPCRb[1:0]

IOPCR[xx]

Pin Control Bits

I/O3B

I/O2B

I/O1B

I/O0B

00 = input

IPR(7), TxC in

IPR(6), RxC in

IPR(3), TxC in

IPR(2), CTSN

01 = output

OPRab(7)

OPRab(6)

OPRab(3)

≠ 01

OPRab(2)

10 = output

TxC 16x

RxC 1x

C/T ab out

TxC 1x

11 = output

TxC 1x

RxC 16x

RxC 1x

TxC 16x

I/O Port Control Channel C (IOPCRC)

IOPCR[xx]

Pin Control Bits

IOPCRc[7:6]

IOPCRc[5:4]

IOPCRc[3:2]

IOPCRc[1:0]

IOPCR[xx]

Pin Control Bits

I/O3C

I/O2C

I/O1C

I/O0C

00 = input

IPR(5), TxC in

IPR(4), RxC in

IPR(0), CTSN

01 = output

OPRcd(5)

OPRcd(4)

OPRab(1)

≠ 01

OPRcd(0)

10 = output

TxC 16x

RxC 1x

RxC 16x

TxC 1x

11 = output

TxC 1x

RxC 16x

RxC 1x

TxC 16x

I/O Port Control Channel D (IOPCRD)

IOPCR[xx]

Pin Control Bits

IOPCRd[7:6]

IOPCRd[5:4]

IOPCRd[3:2]

IOPCRd[1:0]

IOPCR[xx]

Pin Control Bits

I/O3D

I/O2D

I/O1D

I/O0D

00 = input

IPR(7), TxC in

IPR(6), RxC in

IPR(3), TxC in

IPR(2), CTSN

01 = output

OPRcd(7)

OPRcd(6)

OPRcd(3)

≠ 01

OPRcd(2)

10 = output

TxC 16x

RxC 1x

C/T cd out

TxC 1x

11 = output

TxC 1x

RxC 16x

RxC 1x

TxC 16x

The input part of the I/O pins is always active. The programming of the IOPCR bits to 00 merely turns off the out drivers and places

the pin at high impedance.

A read of the IPR register returns the value of the IPR bits as shown above. IPR(5) is at bit position 5 of the data bus. Note that the IPR bit

positions do not follow the 0, 1, 2, 3 order of the I/O ports. During a read of the IPR the I/O ports are not latched. Therefore, it is possible to see

changing data during the read. Port pins that have clocks on them may not yield valid data during the read.

Since the input circuits of the I/O ports are always active it is possible to direct the port signal back into the port. For example: I/O1 will output

the RTS signal. Setting the Counter/Timer (C/T) to be clocked by the I/O1 port will result in the counter counting the number of times RTS goes

active. The change of state detectors on I/O0 and I/O1 will, when programmed, always be sensitive to the signal on the port regardless of the

source of that port’s signal.

NOTES:

1. Normal configurations place RTSN output on I/O1 and place Tx external clock input on I/O3. For the 48 pin Dual In-Line package, I/O3 is

not available. The following options allow flexible I/O programming with the 48 pin package:

When IOPCR(7:6), the I/O3 control,

≠ 00, then I/O1 becomes available to the transmitter as an external clock.

When IOPCR(5:4), the I/O2 control, = 01, then I/O2 may be the RTSN signal if MR1(7) = 1 and OPR(4) = 1.

2. I/O1 becomes RTSN when IOPCR(3:2) = 01 and MR1(7) = 1 and OPR(1) = 1. (OPR(3) for channel B)

Registers of the Interrupt System

The CIR, and “Global” registers are updated with the IACKN signal

or from the “Update CIR” command at hex address 2A. These

registers are not updated when IRQN is asserted since there could

be a long time between the assertion of IRQN and the start of the

interrupt service routine. (See notes following this section).

Current Interrupt Register (CIR)

# Bytes

Type

Chan #

3

3

2

The Channel # field indicates which of the four UARTs has the

highest priority interrupt currently outstanding, while the Type field

indicates its source within the UART. The Type field is encoded as

follows:

000

No Interrupt

001

Change of State

x10

Transmit available

011

Receive available, no error

100

Receiver break change

101

Counter/Timer

111

Receive available, w/errors

With Type = x11, the # Bytes field indicates the count of received

bytes available for reading, while with Type = x10 it indicates the

number of bytes that can be written to the transmit FIFO.

The CIR is Read only at address 28H.