ST68C554 datasheet(5/40 Pages) EXAR

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ST16C554/554D/68C554

Rev. 3.10

SYMBOL DESCRIPTION

Symbol

Signal

Pin Description

type

16/-68

16/68 Interface Type Select (input with internal pull-up). -

This input provides the 16 (Intel) or 68 (Motorola) bus

interface type select. The functions of -IOR, -IOW, INT A-

D, and -CS A-D are re-assigned with the logical state of this

pin. When this pin is a logic 1, the 16 mode interface

16C554D is selected. When this pin is a logic 0, the 68 mode

interface (68C554) is selected. When this pin is a logic 0, -

IOW is re-assigned to -R/W, RESET is re-assigned to -

RESET, -IOR is not used, and INT A-D(s) are connected in

a WIRE-OR configuration. The WIRE-OR outputs are

connected internally to the open source IRQ signal output.

This pin is not available on 64 pin packages which operate

in the 16 mode only.

Address-0 Select Bit. Internal registers address selection in

16 and 68 modes.

Address-1 Select Bit. Internal registers address selection in

16 and 68 modes.

Address-2 Select Bit. - Internal registers address selection

in 16 and 68 modes.

A3-A4

20,50

Address 3-4 Select Bits. - When the 68 mode is selected,

these pins are used to address or select individual UARTs

(providing -CS is a logic 0). In the 16 mode, these pins are

reassigned as chip selects, see -CSB and -CSC. These pins

are not available on 64 pin packages which operate in the

16 mode only.

-CS

Chip Select. (active low) - In the 68 mode, this pin functions

as a multiple channel chip enable. In this case, all four

UARTs (A-D) are enabled when the -CS pin is a logic 0. An

individual UART channel is selected by the data contents of

address bits A3-A4. When the 16 mode is selected (68 pin

device), this pin functions as -CSA, see definition under -CS

A-B. This pin is not available on 64 pin packages which

operate in the 16 mode only.

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