English Amiga Board


Go Back   English Amiga Board > Coders > Coders. Asm / Hardware

 
 
Thread Tools
Old 17 November 2019, 00:34   #1
slingshot
Registered User

 
Join Date: Nov 2019
Location: Budapest/Hungary
Posts: 4
CIA 6526/8521/8520 differences

I searched, but still didn't found a comprehensive list about the differences of the models. What's known by me:
- TOD is binary on 8520 / BCD on others
- Just found this: writing to the timer hi registers when the cra/crb[3] is set (oneshot mode) starts the timer on 8520/don't start on others. This is used during early boot, maybe the reason why a CIA from C64 cannot replace CIAA? Someone else can confirm this?
slingshot is offline  
Old 17 November 2019, 01:12   #2
ross
Per aspera ad astra

ross's Avatar
 
Join Date: Mar 2017
Location: Crossing the Rubicon
Age: 49
Posts: 2,228
Quote:
Originally Posted by slingshot View Post
- TOD is binary on 8520 / BCD on others
Not only is binary (and not BCD) but also with only 3 registers available.
On Amiga, Kickstart use it.

Quote:
- Just found this: writing to the timer hi registers when the cra/crb[3] is set (oneshot mode) starts the timer on 8520/don't start on others. This is used during early boot, maybe the reason why a CIA from C64 cannot replace CIAA? Someone else can confirm this?
Yes, true for 8520.


So 6526/8521 cannot be used on Amiga.
Vice versa 8520 can be used by some extent in C64
(for what I remember the C64 Kernel does not uses the TOD, but I could be wrong because I haven't programmed the C64 for a long time ).
ross is offline  
Old 17 November 2019, 02:45   #3
slingshot
Registered User

 
Join Date: Nov 2019
Location: Budapest/Hungary
Posts: 4
Then I wonder if a 8520 in C64 passes the Lorenz CIA tests (except oneshot). Or the VICE tests (is it has the same timings as the 6526/8521)?
slingshot is offline  
Old 17 November 2019, 12:27   #4
ross
Per aspera ad astra

ross's Avatar
 
Join Date: Mar 2017
Location: Crossing the Rubicon
Age: 49
Posts: 2,228
Quote:
Originally Posted by slingshot View Post
Then I wonder if a 8520 in C64 passes the Lorenz CIA tests (except oneshot). Or the VICE tests (is it has the same timings as the 6526/8521)?
Sure it fail the TOD tests

6526 have also a TODIN bit in CRA not existing in 8520, for accurate time in 50/60Hz.
8520 simply count external event (24-bits): on Amiga CIA-A count 50/60 Hz, CIA-B H-Sync.

For timings you mean operating frequency? I suppose 8520 is rated for 1MHz, underclocked on Amiga at 7xxKhz.
ross is offline  
Old 17 November 2019, 21:56   #5
slingshot
Registered User

 
Join Date: Nov 2019
Location: Budapest/Hungary
Posts: 4
No, I mean internal timings. E.g. after a register write, when the timer actually starts to tick, when it's reloaded exactly and so on. There are a lot of tests for cycle-accuracy of the CIAs in C64, but I'm not aware of anything on Amiga.
slingshot is offline  
Old 18 November 2019, 18:08   #6
ross
Per aspera ad astra

ross's Avatar
 
Join Date: Mar 2017
Location: Crossing the Rubicon
Age: 49
Posts: 2,228
Quote:
Originally Posted by slingshot View Post
No, I mean internal timings. E.g. after a register write, when the timer actually starts to tick, when it's reloaded exactly and so on. There are a lot of tests for cycle-accuracy of the CIAs in C64, but I'm not aware of anything on Amiga.
Well, I can only assume this, but I think the internal timings are the same.
Too few differences to justify something substantial...

However you have to try it
ross is offline  
Old 18 November 2019, 20:48   #7
nogginthenog
Amigan

 
Join Date: Feb 2012
Location: London
Posts: 883
Quote:
Originally Posted by ross View Post
On Amiga, Kickstart use it.
What if you used a 6526 for odd and a 8520 for even CIA (or vice versa). Is TOD used on both chips?
nogginthenog is offline  
Old 18 November 2019, 23:37   #8
ross
Per aspera ad astra

ross's Avatar
 
Join Date: Mar 2017
Location: Crossing the Rubicon
Age: 49
Posts: 2,228
Quote:
Originally Posted by nogginthenog View Post
What if you used a 6526 for odd and a 8520 for even CIA (or vice versa). Is TOD used on both chips?
Unfortunately both CIAs TODs are initialized by the KS.
ross is offline  
Old 19 November 2019, 19:15   #9
slingshot
Registered User

 
Join Date: Nov 2019
Location: Budapest/Hungary
Posts: 4
6526 doesn't work as CIAA because of the Oneshot mode difference (when Kickstart writes to Timer A HI byte, the timer don't start, and it waits forever). But it wasn't tried with real chips, just with FPGA replicas only (however the 6526 model is a very accurate replica).
Reportedly Amiga's 8520 works better in C64. I wonder if anybody tried the VICE tests on it (without the TOD ones).
slingshot is offline  
 


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Similar Threads
Thread Thread Starter Forum Replies Last Post
Tested Amiga 500(+) chips, 8375 Agnus, 8373, 5719, 68000 10 MHz, 8364, 2× 8520, 8371 amiga2000 MarketPlace 0 02 December 2017 12:58
CIA doubts ross Coders. Asm / Hardware 3 09 July 2017 08:44
example of a CIA timer interrupt in assembler using cia.resource Apollo Coders. Asm / Hardware 3 05 July 2013 09:40
CIA test Toni Wilen Coders. General 13 03 March 2007 23:14
A1200 or how to test for a faulty surface mount 8520? gizmomelb support.Hardware 14 10 February 2007 13:01

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +2. The time now is 17:43.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2019, vBulletin Solutions Inc.
Page generated in 0.06897 seconds with 15 queries