[krd: The following instructions were snarfed off the SMUG BBS (since 
demised)]

------------------------------------

From:    Matthew Geier 
To:      All                                      Msg #106, 31-Dec-89 08:12
Subject: UPGRADE YOUR PREMIUM TO A TC PART 1


       OR: How to fit a 256TC keyboard to your premium 'bee

Parts Needed :- 1 x 256TC/Gamma keyboard
                1 x Teleterminal Keyboard interface board - 8507 
Parts Handy  :- 1 x 256TC kernel/boot ROM
                1 x 256TC boot disk
                256/512k memory upgrade

 It also helps to have a circuit diagram of both the premium and the 256TC
handy as a reference. First the background ..

 This modification , which effectively enables your premium to work like a TC
as far as most software is concerned I did to my premium about 2 years ago
now. Since then the orignal keyboard has seen little use , and has decayed to
the point that most of the original keys no longer function.
 The modification is made easy by the fact that the MicroBee Teleterminal
machine was just a premium PC85 , in a new case , with a new keyboard and a
fancy set of ROMs ..
 Looking a page 1 of the 256TC circuit diagrams reveals how the TC keyboard
works. U60 is a decated CPU whos sole aim in life is to scan the keyboard, the
output of this chip is buffered by U61 , and each time the Z80 does a read
from port 0x18 (hex) , a keyboard scan code is returned if one is available.
Some other circuitry based around U71 enable the keyboard CPU to interupt the
Z80 via Bit 1 of PIO channel B when there is a code available to be read. In
this and earlyer microbees this bit is the Cassette output bit , with the TC
ROM altering the data direction on this pin as the need arises. This is what
causes many software incompabilitys , as some programs which need the serial
port reprogram the PIO , and assume that the Cassette Output bit is ALWAYS an
output and program the PIO accordingly. Unfortunatly this is not true of the
TC !

 Now to the premium circuit diagram page 1 ( 8501-4 ) , just under the PIO you
find IC16 , a 76489AN , which happens to be a simple sound synth chip ( I
actually have one of these chips installed ! ). You will notice if you have
the same circuit diagram as mine , a comment under IC16 reading 'wired for
tele-term keyboard'. Its this that makes installation of the keyboard so easy
!. If you have a revision 4 premium , the entire mod consists on fitting a IC
socket to position IC 16 , and plugging in a 16pin ribbon cable to your
keyboard encoder board ( Ensuring that you get it in the right way round !! Be
carefull !)

 If you have a Rev -02 or -03 premium , a few mods to the board need to done
first. This first is to change what was the write signal to the 76489 to be
the interupt line to the PIO , this involves cutting the track leading to pin
5 on IC16 and running a link from Pin5 IC 16 to pin 28 on the PIO ( Which
happens to be nearby .. ).
 The other mod involves changing the port address of IC 16 from 0x10 as used
by the sound chip , to 0x18 as used by the keyboard. This is best done at IC71
where the ports are decoded .. Remove pin 11 of IC71 ( Port 0x10 ) from the
board so that it no longer connects to the PCB and run a short link from IC71
pin 9 ( Port 0x18 ) to the pad on the PCB where pin 11 once lived.
 From there is just a case of plugging the keyboard in as before.

 If you have a TC kernel ROM , replace your orginal Boot rom with the TC
kernel ROM and powerup .. You should be able to then run the self test and
More [Y,n]? 
check out the machine. IF you boot a 56k system disk , it will talk to the new
keyboard , a 128k system disk will ignore the new keyboard. A 256TC disk will
boot and run , on a 128k machine , as LONG AS YOU DONT USE THE RAM DISK !

 The next section is really not about the keyboard - its what else needs to be
done to get 256TC compatablity !

Continued next message ..
                                        
From:    Matthew Geier 
To:      All                                      Msg #107, 31-Dec-89 08:13
Subject: PREMIUM TO TC UPGRADE PART 2

Now for the TC compatablity bit ...

 To get full 256TC function you need at least 256K of memory installed , but
the Peter Broughton upgrade is not compatable with the 256TC as microbee
re-defined the use of a bit on the port 0x50 bank switch latch instead of
using one of the 2 spare bits. The Broughton upgrade uses spare Bits 6 & 7 to
switch the extra banks up to 512k of memory. For only 256K only one extra bit
is needed .. MicroBee , instead of using the next spare bit ( Bit 6 ) , the
re-defined the use of Bit 5 , it was used to bank-switch extra ROMs on the
8342 DRAM core-boards .. As this was only every used 'in house' on a special
set of ROMs they decided to change its use. ( Sound familar ???? ... )

 I worked around this problem by biggy backing a 74LS86 top of IC11 and
connecting it to the existing memory 512k memory upgrade so that Port 50 Bit 5
was XORed with Port 50 Bit 7 , enabling both Broughton's system and microbee's
to work on the same machine. This mod , although probably not the neatest ,
has worked for 2 years quite happly !.
Details - Take a 74LS86 and bend out ALL pins except the power supply pins 7 &
14. I then biggy backed this over IC11 ( only because it was a convenant 14
pin chip ) soldering pins 7 & 14 to there IC11 counter-parts , supplying power
to the LS86. I then ran 2 wires from the 25way X1 connector from pins 23 & 25
to pins 9 & 10 on the LS86 , this connects D5 and D7 to the XOR. I then ran a
wire from pin 8 on the LS86 to where D7 orginally connected to the Broughton
upgrade , in my case D7 was connected to pin14 of the HC174 ( piggy back IC16
) It could equally well have been pin 11 ( Which in my case was D6. Pins 11 &
14 could be swaped around .. )
 That then enables either D5 or D7 to effect the bank switch , keeping both
operating systems happy.
 I have never had any thing to do with a 256k upgrade , but the idea is the
same , only in this case is D5 XOR D6 , as D7 is not used for only 256K. As I
dont know how the 256k upgrade is connected I cant give Pin numbers on where
to connect to the Broughton upgrade - the rest is the same though !.

 The rest of the problem is now software. If running the 256TC system on a
512k machine , you lose access to half your memory. If runing the 512k system
you lose the keyboard. I do know of at least one person running a Broughton
BIOS and a TC keyboard - I dont have the later Broughton Software so I dont
know if it can do this as standard or not.  My machine is currently running a
Custom BIOS written by Philip Hutchision which is giving me access to 512k of
RAM , a 10 meg hard disk AND the Teleterminal keyboard.

[krd: My machine is running the Peter Broughton BIOS with the 256TC 
keyboard... so it is possible. All that is necessary is to use a different 
version of BIOS.SYS to talk to the new keyboard]

 After the above changes , the machine is nearly 256TC hard-ware compatable -
the 256TC has extra character ROM space and another video attribute , but the
extra ROM was never used , and the extra attribute ( Hardware Inverse ) I have
only seen used in the kernel ROM ! ( Self test !! ) [krd: The WS4 VDU 
driver uses this attribute]
 My revison 3 premium has video changes worked out by Philip that give it
256TC video attributes , but I have since long lost the intructions I was
given .. It was a fairly messy operation at any rate and not easy to explain
without circuit diagrams. Its really a mod for the pedantic any way , as it
makes no difference to the compatablity , and the only program I ever recall
using it was the 256TC self test program !.

[krd: Instructions to do this are at the end of this message]

 I have a version 1.15 TC kernal in my premium , I once tryed a latter TC
kernal ROM ( the one without the Network option ) and it would not work .. I
never bothered to figure out why .. So if copying a TC kernal ROM for the
'upgrade' make sure its an old one ! .. Its guarrenteed to work !
 The TC kernal ROM is required if you want 56K CP/M systems , and the microbee
auto-boot protected disks to use the new keyboard , as these systems use the
keyboard routines in the boot rom to scan the keyboard. If you keep the old
ROM installed , these disks will use the old keyboard.
 The 256TC system is also capable of booting from drive B , and as an older
premium boot rom could NOT do this , it DOES NOT INITIALIZE the byte that
tells CP/M d from what drive its booting from. This can result in the TC
system starting to Boot from the A drive , and wanting to finnish the boot
from the B drive !!. Undesirable and confuzing to say the least !. This can be
sort of cured by using the monitor program to fill all of low memory with 0's
first .. ie F 0 fff 0 <CR> I found the cure was a TC kernel ROM ...

 Ill make the usuall disclaimers as to the suitablity of the modifications and
such rubbish. If you break your machine , its still your machine ...

Happy Hacking .... 
                                                                              
---------------------
[krd: The following instructions weren't part of the original message. they 
are included by me for completeness. Again, if you break your machine while 
carrying out the mods, it is still your machine.]

                premium to 256TC part 3 - video attributes

0) Getting the flashing cct to work in the first place.

Parts reqd: IC60 74LS393

[ ] 1.        Install the 74LS393 in the IC60 position.
[ ] 2.        On the component side of the motherboard, cut the track 
leading from the bottom end of C62 down under C63 and IC69 near C62
[ ] 3.        Link one of W6-1 .. W6-4. These set the character flashing 
speed and range from W6-1 () to W6-4 ()

0a) Half-Intensity monochrome display

Parts reqd: 1x 1N914 diode
            1x 680R resistor

[ ] 1.        Fit the diode to the D17 position on the right hand side of 
              the motherboard.
[ ] 2.        Fit the resistor to the R23 position (near D17). The value of 
              this resistor may need changing. I found that a 1K resistor 
              in this position worked best for me.

1) Changing the flashing circuit on the 8501-3 motherboard

The flashing cct on this motherboard is set up so that characters will 
flash normal-inverse rather than on-off. To change this do the following:

NB. If you want hardware inverse, include the steps marked with a '*'
    If you do not want hardware inverse, include the steps marked with a 
    '+'

[ ] 1.        Remove IC69 74LS86
[ ] 2.        Remove IC68 74LS08
[ ] 3.        Break the connection between IC69 pin 12 and the track 
              running next to it.
[ ] 4.        Break the track connecting IC68 pins 2 4 and 5 between pins 2 
              and 4 and between pins 4 and 5.
[ ] 5.        Break the track between IC68 pin 8 and IC69 pin 10 near IC69 
              pin 10
[ ] 6.        Break the track leading to IC69 pin 2 near IC69 pin 2.
[ ] *6.       Break the track connecting IC69 pin 14 IC68 pins 1 and 2 
              between IC69 pin 14 and IC68 pin 1, also between IC68 pins 1 
              and 2.
[ ] 7.        Replace IC69 74LS86
[ ] 8.        Replace IC68 74LS08
[ ] 9.        Join IC68 pin 8 to IC59 pin 11
[ ] 10.       Join IC59 pin 10 to IC69 pin 12
[ ] 11.       Join IC69 pin 11 to IC68 pin 5
[ ] 12.       Join IC68 pin 6 to IC69 pin 2
[ ] 13.       On the underside of the board, join IC68 pin 4 to the pin 
              through between IC69 pins 3 and 4
[ ] +14.      Join IC69 pin 10 to IC68 pin 7
[ ] *14.      Join IC69 pin 10 to IC68 pin 3
[ ] *15.      Join IC68 pin 1 to IC67 pin 1
[ ] *16.      Join IC68 pin 2 to IC39 pin 15

The bits in the attribute RAM will now have the following function

bit   7   6   5   4   3   2   1   0
      ^   ^           ^   ^   ^   ^
      |   |           +---+---+---+-- PCG bank select
      |   +-------------------------- Hardware Inverse
      +------------------------------ Flashing        

2) Extra video attribute and colour RAM

The premium has the capacity to address up to 8k of video RAM. 
Unfortunately many MicroBee programs are written assuming that there is 
only 2K of video RAM fitted. This means that a method of disabling the 
extended video RAM is required. Fortunately this is trivial.

Assuming that your motherboard already has 6264's installed as video 
memory, proceed as follows:

[ ] 1.        Remove the link you will see in the IC43 position.
[ ] 2.        Take a 74LS157, bend pin 15 up and install it in the IC43 
              position.
[ ] 3.        Take a 74LS00 and bendd up all pins except pins 14 and 7
[ ] 4.        Piggyback this 74LS00 on top of a nearby 14 pin IC (IC6 is a 
              convenient one).
[ ] 5.        Join pin 11 of the 74LS00 to pin 15 of IC43 (the bent - up 
              one)
[ ] 6.        Join pin 12 of the 74LS00 to pin 15 IC27 (LV5)
[ ] 7.        Join pin 13 of the 74LS00 to pin 5 IC27 (LV7)
[ ] 8.        Link together pins 9 7 5 2 of the 74LS00

Now the VML bits will have the following functions:

bit  7   6   5   4   3   2   1   0
     ^       ^   ^   ^   ^   ^   ^
     |       |   |   +---+---+---+--- PCG/video bank select             
     |       |   +------------------- Attribute RAM select
     |       +----------------------- Extended SCREEN ram select
     +------------------------------- Premium goodies select

When the extended screen ram is enabled, the 6545 will address all 8k of 
the screen memory. However only 2k at a time will appear in the CPU memory 
map. Screen ram pages are selected by setting bits 2 - 0 in the VML, 
(exactly the same as if you were selecting PCG banks).

I am unsure as to how 256TC compatible this part of the upgrade is. I don't 
know of any software using this extra video RAM.

On cassette premiums, bit 5 of the VML is another ROM select bit (used to 
select which half of basic rom A (a 27128) appears in the memory map at 
8000h). I have not come across any cassette premiums which have the 8k 
screen rams fitted. 

This concludes the discussion.
