This is a WD33C93-based SCSI Controller sidecar unit for the A500 which connects to the A500 side expansion slot. It is the box-like unit with the rounded-front and has two LEDs and a toggle switch in the upper right front-face. Sale began prior to Kickstart 1.3 becoming available, and some early units may not have the Autoboot/RAM card.
The original PCB revision had an option slot for an Autoboot/Memory card. It provides 0/2MB of additional FastRAM and v1.0 Autoboot ROMS under Kickstart 1.3 and higher. The memory type for the memory board was 1Mbit X 1, with 16 chips needed.
The later revision of the controller PCB is identified by the silkscreen label A500-SCSI/4 Rev 3 at the right-rear corner near the SCSI ribbon connector/fan. It takes 2x or 4x of standard 1MBx8 30-pin SIMMs of 120ns or faster, and allows selection of 0/2/4B FastRAM.
Both have an external power supply, and a toggle/game switch which disables only the Autoboot ROM for compatibility with old games. The PSU type is a +5V/+12V/-12V type, with the 5V driving the PCB and HD, the +12v driving the HD motor, and the -12V driving the fan. If a modern +5V/+12V PSU from a GVP Series II or A500 computer PSU, the fan connection must be moved to the other header pins with the +12V marking.
If upgrading the disk to a SCSI2SD-type flash-media unit, one which only uses a 5V power source, there is no need for the fan or any 12v source for the unit.
Sale was discontinued of the Impact SCSI product lne at the introduction of the GVP Series II models based on the DPRC DMA/RAM controller.
Performance and functionality are identical to the original GVP Impact A2000 SCSI+RAM, or the Impact A2000 HC/HC2 products. Improved performance is seen with faster CPUs and with the upgraded FastROM v3.x driver. Compatibility with HDToolbox was also available with the v3.x driver.
This unit can be upgraded with the FastROM v3.x driver ROM if it is placed in the Even (U35) ROM socket. The double-ROM version for the HC2 without the upgraded PAL chip will also work.
Connections:
Green LED - connects to the HDD's activity indicator
Red LED - Connects to CN4
Toggle Switch - Conects to J2 on the Autoboot/RAM card, or the motherboard, depending on the model
AutoConfig IDs:
- 2017/1 - GVP 64K I/O PIC (Impact Series I SCSI)
- 1761 / 8 - GVP FastRAM (2MB/4MB)
4MB Model J1/J3 - RAM Settings (pending info).
J1 on, J3 on - 0MB
J1 off, J3 on - 2MB
J1 on, J3 off - 4MB
J1 off, J3 off - Unsupported
2MB - populate CN9/CN10
4MB - populate CN7-CN10
Memory Type: Standard 1Mx8 30-pin SIMMs (x9 ok, too). 120ns or faster (80ns is typical).
The 2MB Autoboot/RAM card has one additional jumper that toggles 0/2MB - Remove for 2MB after populating the 16x DIP memory positions. Memory type is 1MBx1, 120ns or faster (80ns is typical).
The resistor packs for SCSI termination are soldered onto the main PCB, and the internal disk drive is typicaly mounted as unterminated to allow use of the exteral DB25 SCSI interface. Although this is not exactly SCSI spec, the short 3-4" internal SCSI cable tends to allow this operation without issue.