Specifications

device. A data transfer from processor to memory (always a slave) is “data

out,” and a transfer from memory to processor is “data in.”

TYPES OF DATA TRANSFERS-The type of data transfer being made between

master and slave is determined by the C lines coded as follows:

DATO AND DATOB-The DATO and DATOB operations are

used to transfer

data out of the master to the slave. DATO is used to transfera word to the

address specified by A < .17:01 >. The slave ignores A00 and the

data

pears onD < 15:00>. DATOB is used to transfer a byte of data to the ad-

dress specified by A < 17:OO >. A00 = 0 indicates, the low byte, and

data

appears on D < 07:OO >; A00 = 1 indicates the high byte, and data appears

on D < 15:08 >.

DATI AND DATIP-The DATI and DATIP operations transfer data from a slave

whose address is specified on A < 17:Ol > into the master. Both transfers

are made in words on D < 15:00 >. In destructive read-out devices, DATI

commands a read-write operation, while a DATIP commands a read operation

only and sets a pause flag. When the device receives the subsequent DATO

or DATOB and its pause flag is set, the usual read cycle is skipped and an

immediate write cycle is initiated. Thus, DATlPs are immediately followed

by a DATO or DATOB to effect a read-modify-write data exchange. In non-

destructive read-out devices, DATI and DATIP are treated identically.

This diagram illustrates the data flow in the four data transfers:

DATI OR DATIP

DATA= D<l5:00>

15 8.1 7

SLAM ~~EGISTER

HIGH BYTE , LOW BYTE

DAToBI\AOO

DATOBhm

DATA=D<t5:08 > DATA=D <OX00 >

DATA=CKl5:00>

Figure 8-3 Data Flow

Note that all transfers into the master are word operations; it is up to the

master to accept the appropriate byte. On a DATOB, the master must place

the byte on the appropriate data lines; the slave must accept the proper byte.

DATA TRANSFER EXAMPLES-The bus operations used by the processor for

a typical instruction sequence illustrates how the data transfer operations

are used. The “program” starts at location

1000:

INCB @RO

ADD #3, @RO

where RO contains 500 and location 500 contains 10023. The result of this