CHANGING THE DEVICE NUMBER IN AN MSD DRIVE Latest changes or updates 7-6-05 Quoting from the operators manual, and some added information: CHANGING THE DISK DRIVE DEVICE NUMBER The device number on the MSD SUPER DISK DRIVE (dual: SD2) comes from the factory selected as device number 8, drive number 0 and 1. This is the usual or "default" device number, but if more than one disk drive is to be used with the system, it is necessary to give each disk drive a different device number or drive number. With this disk drive, it is not possible to change the drive numbers (ie 0 and 1), but the device number can be changed using either software (a short BASIC program after power up) or hardware (changing jumpers on the drive PC board). The disk drive determines its device number from a set of jumpers on the PC board inside the drive. At the time the drive is powered on, the jumper settings are "read" by the microprocessor and the resulting number is stored in a specific memory location. This makes it possible to change the default device number by changing (opening or closing) the jumpers. After power up, the device number can be changed by using a "memory-write" command to the memory location that has the device number stored in it. That command must be used each time the drive is turned on. Each method has advantages and disadvantages which will be detailed below. CHANGING THE DEVICE NUMBER BY THE JUMPER (HARDWARE METHOD) 1. Turn off the drive and remove all cables from the drive. 2. Remove six screws from the drive case and remove the top cover. 3. Locate the jumper block JB1 on the top of the PC board near the rear of the drive. It is located between ICs U10 and U11. At that location, there are four solder pads with two bare wire "jumpers" soldered in horizontally. This is the factory configuration for device 8. If JB1-1 is cut (or simply unplugged if a "header" with a removable jumper is installed), the drive will respond as device 9 when powered up. If the jumper at JB1-2 is removed, the drive will be device 10, and with both jumpers removed, device 11. A SPST (single pole, single pole) switch can be installed instead of a jumper to allow the drive to be changed later without opening the case. Note: there is room on the rear of the case for added switches. 4. Replace the case top and install the cabinet screws. Electrically, the two jumpers ground two pins of an IC, namely U22 buffer (74LS240) pins 11 and 17. With a jumper at JB1-1, pin 17 of U22 is grounded, and with a jumper at UB1-2, pin 11 is grounded. This info is helpful in case the solder pads or board traces become damaged and cannot be used. CHANGING THE DEVICE NUMBER BY SOFTWARE The device number can be changed by performing a memory-write to locations $0077 and $0078. The memory-write command is performed after the command channel has been opened with a BASIC statement, usually: OPEN 15,8,15 The memory-write has the following format: PRINT#,"M-W"CHR$(119)CHR$(0)CHR$(2)CHR$(dv+32)CHR$(dv+64) The dv represents the device number that is desired. An example routine for changing the drive from device 8 to device 9 is: 10 OPEN 15,8,15 20 PRINT#15,"M-W"CHR$(119)CHR$(0)CHR$(2)CHR$(9+32)CHR$(9+64) 30 CLOSE 15 To make it easier, this little program can be written to a disk and run each time the number change is needed rather than typing it out every time. The program can be written all on one line by using a colon between statements. It is usually desirable to change the device number in hardware unless a temporary change is all that is needed. In order to use the software method, only one drive can be powered on, its device number changed, then the next drive powered on and its device number changed, until all drives are on. If this procedure is not followed, there will be a device "conflict" on the serial bus and the drives will not work reliably or at all. SOME ADDED NOTES FOR THE MSD-SD2 DRIVE In my SD2, the PC board tends to bow outward physically towards the metal case. I didn't want a short circuit to damage the drive, so I installed a 6" X 6" cardboard spacer to keep the board away from the case top. A sheet of thick plastic glued to the inside of the case top would work as well. The original cabinet screws were missing when I got my SD2. I noticed that if the replacement screws were any longer than about 1/4", they would hit the PC board inside. The important ones are the three on the side of the case away from the drive mechanisms and closest to the PC board inside. ERROR FLASH CODES FOR THE SD2 (seen at power up if there is a fault) Number of flashes Suspected component failure 1 Micro U7 2 RAM U1 3 RAM U2 4 RAM U3 5 ROM U5 6 ROM U6 7 Drive mechanism Ray Carlsen CET Carlsen Electronics... a leader in trailing-edge technology