AMX 68000, Target Guide

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AMX 68000 Target Guide

If your clock can be serviced by writing one or two n-bit values to a device I/O port, you

can use the ...CLKFAST directive to create a very fast clock ISP root with no application

code required. The general form of the ...CLKFAST directive is as follows.

...CLKFAST CLKROOT,CLKADR,CLKCMD,CLKADR2,CLKCMD2,IODELAY,VNUM

CLKROOT Name of the clock ISP root entry point

CLKADR 32-bit numeric device memory address

CLKCMD 8-bit numeric command

CLKADR2 32-bit numeric secondary device memory address

CLKCMD2 8-bit numeric secondary command

IODELAY Delay (µs) required between I/O commands

VNUM Interrupt vector number assigned to the clock device

The numeric parameters must be expressed in a form acceptable to your assembler.

Parameters CLKADR2, CLKCMD2, IODELAY and VNUM can be omitted if they are not required.

If a parameter is omitted, its field must be left blank (empty) and the comma to the left of

the field must be retained. If the resulting ...CLKFAST directive ends with a string of

commas because the intervening parameters have all been omitted, it is acceptable to

delete the trailing commas.

The clock ISP root will dismiss the clock interrupt by writing the 8-bit value CLKCMD to

the 32-bit device memory address CLKADR. If parameter CLKADR2 is present in the

...CLKFAST directive, the clock ISP root will then write the 8-bit value to the 32-bit

device memory address CLKADR2. If parameter CLKADR2 is present, parameter CLKCMD2

must also be present. If this second device I/O command is not required, leave both

CLKCMD2 and CLKADR2 blank (empty).

If two I/O commands are provided, parameter IODELAY can be used to define the delay, if

any, required after the first command before the second command can be issued. The

delay is provided by a call to AMX procedure cjcfhwdelay (see directive ...DELAY).

If there is no need for a delay or a second command is not required, leave the IODELAY

field blank (empty).

Parameter VNUM has been described on the preceding page. If parameter VNUM is omitted,

then a value of -1 is assumed for VNUM.

Use the ...CLKFAST16 directive if 16-bit values must be written to the clock.

Use the ...CLKFAST32 directive if 32-bit values must be written to the clock.