TS68HC901 datasheet(8/42 Pages) STMICROELECTRONICS

8 / 42 page

interrupt structure is not implemented, the IEI of all

CMFPs must be tied low.

When the processor initiates an interrupt acknow-

ledge cycle by driving IACK and DS, the CMFP

whose IEI is low may respond with a vector number

if interrupt is pending. If this device does not have a

pending interrupt, IEO is asserted which allows the

next lower priority device to respond to the interrupt

acknowledge. When an CMFP propagates IEO, it

will not drive the data bus nor DTACK during the in-

terrupt acknowledge cycle. The timing for an IACK

cycle is shown in figure 23 and 24.

RESET OPERATION

The reset operation will initialize the CMFP to a

known state. The reset operation requires that the

RESET input be asserted for a minimum of two

microseconds. During a device reset condition, all

internal CMFP registers are cleared except for the

timer data registers (TADR, TBDR, TCDR and

TDDR), the USART data register (UDR), the trans-

mitter status register (TSR) and the interrupt vector

ceiver and transmitter are disabled. The interrupt

channels are also disabled and any pending inter-

rupts are cleared. In addition, the general purpose

interrupt I/O lines are placed in the high- impedance

input mode and the timer outputs are driven low. Ex-

ternal CMFP signals are negated. The interrupt vec-

tor register is initialized to a 0Fh.

NON MULTIPLEXED MODE

In this mode, the MPX input must be set to zero, and

the TS68HC901 can be used with a 68000 proces-

sor type or a 6800 processor type. Refer to figure 21

to 24 for the electrical characteristics.

With a 6800 processor type the DS pin is connected

to the E signal of the processor, the DTACK signal

is not used and the CLK must be zeroed.

MULTIPLEXED MODE

The CMFP can be used either on a MOTOROLA or

INTEL bus type. In this case the MPX pin is connec-

ted to Vcc. The table page 4 gives the signification

of the different signals used. A dummy access to the

TS68HC901 has to be done before any valid access

in order to set up the internal logic of sampling.

TS68HC901

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