Types of memory
There were several types of memory being used when the Z88 came out. The Z88 uses static RAM. This was the only low power type but it was extremely expensive when the Z88 came out (£200 for 1M). With the demand for portable computers, the prices have fallen. The Z88 never turns itself off. It gives a pulse every 20 seconds to keep the information stored in RAM intact. There is only one way to see if different RAM chips will work with the Z88 in these different environments is to try them.
RAM Test |
Cambridge Computer wrote a BBC BASIC program to test the RAM.  Image Added
Unless the memory is good the Z88 will become unstable, the FAIL indicator may appear in the top right-hand corner of the display or inconsistent results will occur when checking the size of the RAM with (<>  Image Added CARD). For example, you may have a 512K Ram RAM card in your Z88 but (<> Image Added CARD) reports that you only have 128K. Failure of the RAM falls in into the following categories. - Mechanical failure - due to the contacts being dirty or from a dry soldered joint
- Unsuitable memory chip - if a different chip is used it may not have the identical specification to the one previously used.
Running the BASIC program while `tapping' the RAM pack may identify a mechanical failure. Finding other errors can be difficult. The other sort of memory failure is where certain bits of memory suffer amnesia when you are not reading or writing to the memory. This is like when you are just storing files in the RAM. This fault can be found with any program, (zCheck, Zip, Unzip (Z88 Forever) or SqueeZ~88 (Rakewell)) that uses checksums on files. To use it you should:- - Run the program initially so that the checksums of the files are calculated. If you are using SqueeZ~88 or Zip, squeeze/Zip a load of big files.
- Turn off the Z88 and leave it alone for about three to five days.
- Re-run the program to see if the checksums of the files are different or unsqueeze/Unzip all the files again. If they are, then the RAM where the file was stored is faulty.
The following BBC BASIC program tests 32K, 128K 512K and 1MB Ram packsRAM cards. It is what This is called a destructive Ram Test which means that all RAM Test. All the data that is stored on in the RAM card will be destroyederased. Download the 4 files zipped, (original instructions, two .CLI files (which do the same thing) and the memory test software from here, and then transfer them to your Z88 with a transfer program. .  Image RemovedIf the CLI file is in an EPROM in slot 3, Image Added There are two ways you can use this program. - Just running the BBC BASIC program (Ramcard.bas)
- Before using the program you should save the program to EPROM as "RAMTEST.BAS" and write the following BOOT.CLI to use with it. This will load and run the program automatically after a HARD RESET is given.
#F
|EF
RAMTEST.BAS~E~E
#B
CHAIN
"RAMTEST.BAS"~E to do To use the memory test, do the followingfollow these steps:- | | | |
|---|
| Image Modified | | Prepare Save onto an EPROM with card the BOOT.CLI and RAMTEST.BAS files. |  | | Back-up all your files. | | Image Modified | | Open the card flap Remove the current RAM packcard. | | Image Modified | | Insert the EPROM card in slot 3 | | | Do a Hard Reset. | Leaving the card flap open, - do a Hard Reset.
- Close the card flap
The BOOT.CLI program will run, the memory test programs will be fetched from the EPROM card and then will start to run.
 Image Added
| | | |  Image Modified
When you get the Command line type in the number of K the ram RAM card is. E.g. 1024  Image Modified
| | Image Modified | | Insert the RAM card to be tested in Slot 1. | | | |  Image Modified
Press the ENTER Image Added key until you get the "Testing . . . " message. Whilst this is testing, tap underneath the Z88 where the card is installed to expose any mechanical electrical problems with the card connector and/or any dry solder joints in the card itself. | | | |  Image Modified
When the test is finished, | | Image Modified | | Remove the EPROM pack and | | | | Do another Hard Resetanother Hard Reset. | | | | To make sure that the memory is alright, load a large text file into Pipedream and see if you can read the whole file. |
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Technical Specification of a Flash and RAM chips
Results updated 17th August 2013
| | | Z80 4MHz | A29040B Flash | BS62LV8001 | AS6C8008 | LY62W10248-55 | CY62158ELL-45ZSXI |
|---|
Supply Voltage Min | V | | | 2.4 | 2.7 | 2.7 | 4.5 |
| Supply Voltage Typ | V | | | - | 3.0 | 3.0 | 5.0 |
| Supply Voltage Max | V | | | 5.5 | 5.5 | 5.5 | 5.5 |
Input High Voltage | V | 2.2 to VCC | 0.7 x VCC min to VCC+0.3 | 2.2 to VCC+0.3 | 2.4 to VCC+0.3 | 2.4 to VCC+0.5 | 2.2 to VCC + 0.5 V |
Input Low Voltage | V | -0.3 to 0.8 | 0.5 to 0.8 | -0.5 to 0.8 | - 0.2 to 0.6 | - 0.2 to 0.6 | –0.5 to 0.8 |
Output High Voltage | V | 2.4 min | 0.85 x VCC | 2.4 min | 2.4 min | | 2.4 min |
Output Low Voltage | V | 0.4 max | 0.45 | 0.4 max | 0.4 max | | 0.4 max |
Standby Power | uA | | 1 | 3.5 to 50 | 6 to 80 | 10 to 50 | 2 to 8 |
| Power Consumption | mA | | 20 - 40 | 39 | 60 | 30 to 60 | 1.8 to 3 |
VCC for Data Retention | V | | | 1.5 | 2.0 | 1.5 | 2.0 |
| Read Timings | | | | | | | |
|---|
| Read Cycle Time tRC | ns | | 55 min | 55 min | 55 min | 55 min | 45 min |
| Address Access Time tAA | | | 55 min | 55 max | 55 max | 55 max | 45 max |
Chip Enable Access Time tACE | | | 55 min | 55 max | 55 max | 55 max | 45 max |
| Output Enable Access Time tOE | | | 30 max | 25 max | 30 max | 30 max | 22 max |
| Chip Enable to Output in Low-Z tCLZ | | | 18 min | 10 min | 10 min | 10 min | 5 min |
| Output Enable to Output in Low-Z tOLZ | | | 18 min | 10 min | 5 min | 5 min | 10 min |
| Chip Disable to Output in High-Z tCHZ | | | | 30 max | 20 max | 20 max | 18 max |
Output Disable to Output in High-Z tOHZ | | | | 25 max | 20 max | 20 max | 18 max |
Output Hold from Address Change tOH | | | 0 | 10 min | 10 min | 10 min | 10 min |
| Write Timings | | | | | | | |
|---|
Write Cycle Time tWC | | | 55 min | 55 min | 55 min | 55 min | 45 min |
Address Valid to End of Write tAW | | | 40 min | 40 min | 50 min | 50 min | 35 min |
Chip Enable to End of Write tCW | | | | 0 | 50 min | 50 min | 35 min |
Address Set-up Time tAS | | | 0 | 40 min | 0 | 0 | 35 min |
Write Pulse Width tWP | | | 20 min | 30 min | 45 min | 45 min | 35 min |
Write Recovery Time tWR | | | 0 | 0 | 0 | 0 | |
Data to Write Time Overlap tDW | | | 25 min | 25 min | 25 min | 25 min | 25 min |
Data Hold from End of Write Time tDH | | | 0 | 0 | 0 | 0 | 0 |
Data Setup to Write End | | | | | | | 25 min |
Output Active from End of Write tOW | | | | 5 min | 5 min | 5 min | |
Write to Output in High-Z tWHZ | | | | 25 max | 20 max | 20 max | 10 max |
| | | THE Z80 CPU :
TIMING | | | | | |
RAM Chips that have failed
LYONTEK - LY62W10248ML
This is the exchange between Rakewell and LYONTEK to find out why their RAM chip fails.
...
I have uncompressed files, and have saved files to the flash chip. The failure occurs when I am loading a larger file into the word-processor. The Z88 displays a “fail” message which is associated to a memory failure of some sort (usually if the RAM is removed from the slot).
ALLIANCE MEMORY - AS6C8008-55ZIN
ALLIANCE MEMORY - AS6C8008-55ZIN - SRAM, 8MB, 2.7-5.5V, 1024KX8, TSOP44
TESTED FAILS
This chip fails the memory test consistently.