SC68C198 datasheet(5/49 Pages) PHILIPS

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Philips Semiconductors

Product specification

SC26C198 SC68C198

SC26L198 SC68L198

Octal UART with TTL compatibility at 3.3V

and 5V supply voltages

1995 May 1

340

BLOCK DIAGRAM

Block Diagram SC26/68C198

FULL DUPLEX UART CHANNEL

INPUT BUFFERS AND OUTPUT DRIVERS

SD00193

As shown in the block diagram, the Octal UART consists of: an

interrupt arbiter, host interface, timing blocks and eight UART

channel blocks. The eight channels blocks operate independently,

interacting only with the timing, host I/F and interrupt blocks.

FUNCTIONAL DESCRIPTION

The SC26C198 is composed of several functional blocks:

• Synchronous host interface block

• A timing block consisting of a common baud rate generator

making 22 industry standard baud rates and 2 16–bit counters

used for non–standard baud rate generation

• 4 identical independent full duplex UART channel blocks

• Interrupt arbitration system evaluating 24 contenders

• I/O port control section and change of state detectors.

CONCEPTUAL OVERVIEW

Host Interface

The Host interface is comprised of the signal pins CEN, W/RN,

IACKN, DACKN, IRQN Sclk and provides all the control for data

transfer between the external and internal data buses of the host

and the OCTART. The host interface operates in a synchronous

mode with the system (Sclk) which has been designed for a nominal

operating frequency of 33 MHz. The interface operates in either of

two modes; synchronous or asynchronous to the Sclk However

the bus cycle within the OCTART always takes place in four Sclk

cycles after CEN is recognized. These four cycles are the C1, C2,

C3, C4 periods shown in the timing diagrams. DACKN always

occurs in the C4 time and occurs approximately 18 ns after the

rising edge of C4.

Addressing of the various functions of the OCTART is through the

address bus A(7:0). The 26C198 is compatible with the SC28L194

Quad UART in software and function. A[7], in a general sense, is

used to separate the data portion of the circuit from the control

portion.

Asynchronous bus cycle

The asynchronous mode requires one bus cycle of the chip select

(CEN) for each read or write to the chip. No more action will occur

on the bus after the C4 time until CEN is returned high.

Synchronous bus cycle

In the synchronous mode a read or write will be done every four

cycles of the Sclk. CEN does not require cycling but must remain

low to keep the synchronous accesses active. This provides a burst

mode of access to the chip.

In both cases each read or write operation(s) will be completed in

four (4) Sclk cycles. The difference in the two modes is only that the

asynchronous mode will not begin another bus cycle if the CEN

remains active after the four internal Sclk have completed. Internally

the asynchronous cycle will terminate after the four periods of Sclk

regardless of how long CEN is held active

In all cases the internal action will terminate at the withdrawal of

CEN. Synchronous CEN cycles shorter than multiples of four Sclk

cycles minus 1 Sclk and asynchronous CEN cycles shorter than four

Sclk cycles may cause short read or write cycles and produce

corrupted data transfers.

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