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Forum:
Hardware
Beiträge im Thema:
7
Erster Beitrag:
vor 2 Jahren, 9 Monaten
Letzter Beitrag:
vor 2 Jahren, 5 Monaten
Beteiligte Autoren:
Dennis Kuschel, Randolpha, Michael Schoettner

Micro code control board

Startbeitrag von Michael Schoettner am 31.05.2015 14:24

Dear all,

I have some question regarding the micro code control board and its connectors. Many thanks in advance for any help.

Best regards,

Michael


Related to V4 (going to the signal decoder)[/b]

1)
BUSCLK2
Is this for the external or internal bus?

2)
/BUSCLK2
What is the purpose of the inverted signal?

3)
TSEI
?

4)
TIPC
?

5)
RES.PC
Reset program counter?

6)
TCLI
Something related to interrupts?


Related to V1 (going to bus & register control)

1)
BUSCLK1
Is this for the external or internal bus?

2)
/BUSCLK1
What is the purpose of the inverted signal? Same as above for V4.

3)
TOP
Low and high byte for 16 bit read/write control line?

4)
OECOD
Output code to external bus and insert wait state? Code = command/request?

Antworten:

Hi Michael,

Related to V4:

1) BUSCLK2
is the same signal like BUSCLK1 and BUSCLK. Same signal, but other name in the PCB file.
It is for the internal data bus.

2) /BUSCLK2
is the same signal like /BUSCLK1 and /BUSCLK. It is the inverted version of BUSCLK. Because of propagation delays some Flip-Flops must be clocked on the falling clock edge to ensure the required set-up time, so this signal was introduced.

3) TSEI
a low level on this signal enables interrupts.

4) TIPC
When this signal is low, the program counter gets incremented within the current clock cycle.

5) /RES.PC
This signal resets the program counter so program execution starts at address 0.

6) TCLI
a low level on this signal disables interrupts.


Related to V1:

1) BUSCLK1
is the same signal like BUSCLK. It is for the internal data bus.

2) /BUSCLK1
is the inverted version of BUSCLK

3) TOP
When this signal is asserted low in the current clock cycle, a new OP-Code is fetched into register IC8.

4) OECOD
is the internal name for the signal /RDCODE on the backplane bus connector. This signal is asserted low when the CPU wants to read data from ROM memory (= program code memory) instead from RAM memory.

Regards,
Dennis

von Dennis Kuschel - am 31.05.2015 16:06
Dear Dennis,

thank you very much for your fast reply! I am trying to understand all PIN connectors on the CPU boards to learn how the CPU boards work together. I also searched you old web pages but did not find this.

I write these things down and can share this here, if you think this would be useful for the community. If so, it would be good, if you could check this before release :)

Or is it already written down somewhere?

Best regards,

Michael
--

von Michael Schoettner - am 31.05.2015 18:00
Hi Michael,

I'd be very thankful if you could write down what we have worked out together. The description of the internals of MyCPU is still missing on my webpages.

Of course I will have a look to your elaboration before publishing.

Kind Regards,
Dennis

von Dennis Kuschel - am 02.06.2015 10:52
Dear Dennis,
How can I better understand microcode state machine? Can you give me some notes?
Thanks a lot.

von Randolpha - am 15.09.2015 12:29
Hi Randoplha,

the microcode is stored in the EPROMs IC1, IC2 and IC3. The EPROMs have four types of inputs: 1) the currently executed OP-Code, 2) a counter value that counts from 0 to 31, 3) the processor flags and 4) the state of the interrupt level (a hardware interrupt is going to be executed or not). Each OP-Code can have up to 32 microcode steps, defined by the counter input 2). Dependent on the four inputs to the EPROMs different output signals are generated. The outputs control mainly the data flow within the CPU, that means the source and the destination of a data transfer. Also some control signals are generated to (for example) increment the program counter or load and store data from/to external memory. Since the EPROMs are used as large look-up-tables in MyCPU, it is not so easy to understand whats going on. I have written a simple microcode compiler that has helped me to write the microcode. Please have a look to the attached text file, it is an excerpt of the microcode source file that contains the microcodes for all 256 OP-Codes.
[attachment 62 mcode_excerpt.txt]

von Dennis Kuschel - am 15.09.2015 14:31
Dear Dennis,
Thanks for your help.

von Randolpha - am 17.09.2015 11:36
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