procedure clearRecord;

The function clearRecord() removes all data from internal memory and fills it with zeroes (0x00) or spaces (0x20).
You can call this function before calling setField(), setMemoBuf().

begin
    // your code
    dbf.clearRecord;
    dbf.setField(0, 'some value', 0);
    dbf.setField(1, nil, 123.45);
    dbf.appendRecord(False);
    // your code
end;