On 2017-12-17 13:04, Johnny Billquist wrote:
On 2017-12-17 12:56, Johnny Billquist wrote:
On 2017-12-17 01:20, Tim Stark wrote:
Folks,
Well, there are some PDP-11 tech docs indicates that higher models
like 11/53, 11/73, 11/74, 11/83, 11/84, 11/93, and 11/94 have
built-in own firmware ROMs at starting 160000 with switch bits for
banking.
As Christian said, the 11/74 is not correct to include in this
discussion, as it is in a different family.
All the others are J11 based machines, and somewhat similar.
Also, some variant of the 11/73 used a double height module, which did
not include any boot roms, so that one does not have anything around
this.
I can't remember how the 53, 83 and 84 works straight up, but I just
went back and checked the 93 and 94. I think the others work the same,
but someone should check.
Anyway, the 93 and 94 have an 8K EEPROM, which obviously is too big to
all fit at the same time in the I/O page. However, it does not map
into 160000 ever. There are two memory areas in the I/O page set aside
for boot roms.
165000, holding 512 bytes.
173000, holding 512 bytes.
Usually 165000 holds self diagnostics, and the common code for
booting, while 173000 holds device specific booting code.
The KDJ11 module can use neither, one, or both of these areas. If
165000 is enabled, it holds the basic, common code, which can then
also boot using traditional M9312 boot roms, located in 173000. For
this, the KDJ11 needs to disable its own use of 173000. If you have
some module with its own booting in general, which uses 165000, you
also should disable the KDJ11 use of that area (obviously). The
enabling and disabling of the use of these areas are controlled by a
CSR at 177520 (there don't seem to be a specific name for that CSR).
If the KDJ11 use either of these areas, they are bank switched. The
KDJ11 creates the full address into the EEPROM by using the low 9 bits
from the physical address, and the high bits come from a register
called PCR (177522). One byte is used for the 165000 area, and one
byte for the 173000 area.
All this is documented in the 11/93 and 11/94 manuals.
And to correct myself. When I write EEPROM I was short-circuiting
myself. There is both a ROM and EEPROM on the module. And for 165000,
when enabled, the access can go either to ROM or EEPROM. And the ROM is
the 8K. Select of ROM or EEPROM is also done through the CSR at 177520.
And I need to proofread things before sending.
Also, 173000 is always ROM. EEPROM is only a possible option for the
165000 area, and at power on, it will be the ROM that is accessed.
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: b...@softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
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