MK68901 datasheet(2/33 Pages) STMICROELECTRONICS

2 / 33 page

necessary control and status interface to the pro-

grammer.

The MFP is a derivative of the MK3801 STI, a Z80

family peripheral.

PIN DESCRIPTION

GND :

Ground

VCC :

+5 volts (

± 5%)

CS :

Chip Select (input, active, low). CS is u-

sed to select the MK68901 MFP for ac-

cesses to the internal registers. CS and

IACK must not be asserted at the same

time.

DS :

Data Strobe (input, active low). DS is u-

sed as part of the chip select and interrupt

acknowledge functions.

R/W :

Read/Write (input). R/W is the signal

from the bus master indicating whether

the current bus cycle is a Read (High) or

Write (Low) cycle.

DTACK : Data Transfer Acknowledge. (output, ac-

tive low, tri-stateable) DTACK is used to

signal the bus master that data is ready,

or that data has been accepted by the

MK68901 MFP.

A1-A5 :

Address Bus (inputs). The adress bus is

used to adress one of the internal regis-

ters during a read or write cycle.

D0-D7 :

Data Bus (bi-directional, tri-stateable).

The data bus is used to receive data from

or transmit data to one of the internal re-

gisters during a read or write cycle. It is

also used to pass a vector during an in-

terrupt acknowledge cycle.

CLK :

Clock (input). This input is used to pro-

vide the internal timing for the MK68901

MFP.

RESET : Device reset. (input, active low). Reset

disables the USART receiver and trans-

mitter, stops all timers and forces the ti-

mer outputs low, disables all interrupt

channels and clears any pending inter-

rupts. The General Purpose Interrupt/I/O

lines will be placed in the tri-state input

mode. All internal registers (except the ti-

mer, USART data registers, and transmit

status register) will be cleared.

INTR :

Interrupt Request (output, active low, o-

pen drain). INTR is asserted when the

MK68901 MFP is requesting an interrupt.

INTR is negated during an interrupt ac-

knowledge cycle or by clearing the pen-

ding interrupt(s) through software.

IACK :

Interrupt Acknowledge (input, active

low). IACK is used to signal the MK68901

MFP that the CPU is acknowledging an

interrupt. CS and IACk must not be as-

serted at the same time.

IEI :

Interrupt Enable In (input, active low). IEI

is used to signal the MK68901 MFP that

no higher priority device is requesting in-

terrupt service.

IEO :

Interrupt Enable Out (output, active low).

IEO is used to signal lower priority peri-

pherals that neither the MK68901 MFP

nor another higher priority peripheral is

requesting interrupt service.

10-17 :

General Purpose Interrupt I/O lines.

These lines may be used as interrupt in-

puts and/or I/O lines. When used as in-

terrupt inputs, their active edge is pro-

grammable. A data direction register is u-

sed to define which lines are to be Hi-Z

inputs and which lines are to be push-pull

TTL compatible outputs.

SO :

Serial Output. This is the output of the U-

SART transmitter.

SI :

Serial Input. This is the input to the U-

SART receiver.

RC :

Receiver Clock. This input controls the

serial bit rate of the USART receiver.

TC :

Transmitter Clock. This input controls the

serial bit rate of the USART transmitter.

RR :

Receiver Ready. (output, active low)

DMA output for receiver, which reflects

the status of Buffer Full in port number

15.

TR :

Transmitter Ready. (output, active low)

DMA output for transmitter, which re-

flects the status of Buffer Empty in port

number 16.

TAO,TBO,

TCO,TDO:

Timer Outputs. Each of the four timers

has an output which can produce a

square wave. The output will change

states each timer cycle ; thus one full pe-

riod of the timer out signal is equal to two

timer cycles. TAO or TBO can be reset

(logic ”O”) by a write to TACR, or TBCR

respectively.

XTAL1,

XTAL2 :

Timer Clock inputs. A crystal can be

connected between XTAL1 and XTAL2,

or XTAL1 can be driven with a TTL level

clock. When driving XTAL1 with a TTL le-

MK68901

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