Re: HP-HIL and USB


Paul Bicknell
 

Hi Chris

 

The item that is urgently required is a standard keyboard interface to HP-HIL

Ie   USB to HP-HIL

 

Regarding the HP-HIL mail connectors not a problem there are 2 types 

 

1 Dot   Type   A   part number  1-1761184-1-ND  this goes into the keyboard

2 Dot   Type   E   part number  5-1761184-1-ND  this goes into the equipment

 

Last time I looked  digeky  had over 200 of each

 

Paul


From: VintHPcom@groups.io [mailto:VintHPcom@groups.io] On Behalf Of Chris Hanson
Sent: 14 December 2019 22:13
To: VintHPcom@groups.io
Subject: [VintHPcom] HP-HIL and USB

 

On Dec 12, 2019, at 10:24 AM, Dave via Groups.Io <dfnr2@...> wrote:

 

I think the USB to HIL interface would probably be the easiest and cheapest option.

 

I’ve looked into building a HP-HIL to USB interface a bit and it’s going to be a little bit of work:

 

I. Connections

Sourcing the connectors and cabling for HIL is difficult. And the connectors are rare enough that taking things apart to use their HIL connectors isn’t really a good idea. (Except maybe ID boxes.) At least the “HIL extender” systems use DB-15 on one side so you can use that as an endpoint without dismantling anything.

 

II. Hardware Interfacing

I recall the voltage levels involved in HIL being slightly different than TTL, which means building custom level shifters out of transistors. At least getting transistors that cleanly switch at 200+ KHz shouldn’t be difficult.

 

III. Low-level protocol

The low-level protocol for HIL is trivial—it’s basically just bidirectional serial with a start bit, stop bit, and parity—but you can’t get off-the-shelf hardware to speak it because it’s an un-clocked 100kbps protocol with 15-bit packets and pretty strict timing requirements. So you’re looking at making your own UART either with bit-banging or logic. This gives, for example, a 16MHz Arduino approximately 160 clock cycles per bit—which doesn’t give it time for much else, especially since you need to be able to both transmit and receive.

 

IV. High-level protocol

Once you get packets going back and forth, this part is easy; there are plenty of examples in NetBSD et al, in addition to what’s in the HP-HIL protocol reference. Building an API to talk to devices and translate them to something modern should be straightforward if everything else is taken care of.

 

The approach that I’ve planned to take whenever I try this again is to use an AVR or two solely as a custom UART since 160 cycles/bit should easily be sufficient for a polled/bit-banged software UART implementation, with room enough to implement a couple of registers and buffers accessible by the actual host device, which would be something more like a Cortex M series that implements the high-level protocol and USB HID.

 

In other words:

 

USB HID <—> Cortex (HID/HIL) <—> AVR (custom UART) <—> DB-15 HIL

 

Make sense?

 

  — Chris

 

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