Firmware Update 2022

First a completely new CPLD design has been created. Instead of various select and clock signals I have decided to greatly simplify the interface between the CPLD and the MCU. To address registers you need now to first load the register address to the CPLD. The signal ALER is used to set the register read address and ALEW is used to set the register write address. There are two signals as there are two CPLDs. One for the read registers and one for the write registers.

Afterwards you can either RD or WR the addressed register. Internally the register address is then advanced automatically to the next useful address. This interface uses a few MCU cycles more but uses less interface PINs and is more consistent.

The next major difference is the handling of seek. Previously a lot of the seek processing has been done in the interrupt service routine to allow handling of the seek operation in software without disabling the controller. However this is not true for the real RLV12. For a short period after executing a seek function the controller will be busy until it has sent the seek command to the disk drive. The command is sent via a serial line clocked by a 4MHz clock and as a command uses 16 bits this will take at least 4usec for the controller to send the command. Once the command has been sent the controller will be ready to accept further commands while the disk drive executes the seek. This is now handled the same on the RLV12 emulator. A seek command will set the controller busy and the seek command will be executed in the same function dispatching process. Of course there is not much to be done and the drive will be ready again after a very short period.

Next all unneccessary references to other RLV12 emulator versions or models have been removed and the code has undergone a serious restructuring and clean-up.

Last but not least a so called autoboot feature has been added, by simply executing a 174414G command in ODT the controller will boot the OS from the first unit.

Firmware Update 2024

I managed to screw up my source repository and made a mess, as I was using part of the RLV12 Emulator firmware in my DiskEMU project and thought it was a good idea to backbport bug fixes and design changes made in the DiskEMU project to the RLV12 Emulator without tracking the changes. I barely managed to restore a working HEX file with a working release of the 2022 update.

After some feedback from other users I decided then to make a new release with some features added in my DiskEMU project. Most notably I added the BootROM option, you can activate a ROM image at address 173000 in the PDP‐11 IO‐page. This allows the CPU to be set to autostart from the address 173000. The boot ROM will be made loadable and configurable.

The hardware does not require any changes. And if you want an activity LED you still need the ECO wire mentioned in the description later. However this is optional.

Schematic Update 2024

This update still uses exactly the same hardware as the first version of the RLV12 Emulator V2.0. However I have changed the interface between the MCU and the CPLDs. As a result I changed the schematic to reflect the new signal names. In other words the drawing changes but the PCB did not.