Sinclair ZX81 - Page 16

INCREMENTAL SERIES RUMIWG ALONGSIDE OTHER MEMORIES 3
General Notes;
All 5AM pack add-ons of 16K or over known to us (except for our own) have a built-
in disable of the original IK RAM on tho ZX81 board. Henoe it is not possible to use
the IK RAM on the ZX81 board if such- an external memory is in use. As well as this it is
necessary to roake the Incremental RAM selection agre* wdth the •ea-Uiriial fIwyaas^c - ie the ZE
plug must be set for dibble (see Appendix B).
Also, it should be understood
s
that the decoding for the IK and 16K RAMS that exist
in the ZX81 is only partial and ignores bit 15 of tho address. If the total RAM is not mor<
than 16K it is as a result of this necessary to mask bit 15 of the address to the Tp^rsTnTr
decoding and this is the purpose of positions 25 and 26 on the plug-and-sookei switches.
Clearly, if more than 16K RAM exists on the system it will be necessary to usa bit 15 to •
differentiate "between 16K blocks. Please refer to Appendix B for Jaoatiiogs «£. suujjjzh. setting
abbreviations.
Note - In the following table of switch settings NCroeand- No eh-iage from the correct
setting for Incremental memory running on its own,
MBSA ZRS BBS TRS
6K KAM packs
e.g. Sinclair, Audio Computers etc. 5 18 NG 2$
32K RAM packs,
e.g. Audio Computers. Pins 3
a
nd 14 Of 1C3 "
cn
Audio Computer board should be directly connected to
place second (16K$ half of 32K at top of memory (ie
from address * "'\ to 64K so that Incremental memory can be
placed in between the halves giving 48K of continuous memory. 5 ' 18 U\ 26
48K RAM p_acks.
e.g. Jfefflo-t&sli.. The remaining- 8K of tho ^-1^ =^A»aao
CTI
w«>» J-js4jo.
s
between th« 6K -fi©M snri ti»« 4GK KAH can bo occupied by the
Ino3reni©fital board with the following switch settings to give
the majtimuB possible directly addresacsd EAL. of 56K, 2 18 22,^4 £$
6K RAM packs.
Sinclair? Others? The Incremental can be placed iramGdiately
above as follows. 4 18 2£
}
24 ?5
Others
Please call us for advice on any other packs th-it vnn ^*r
rrm*. a-»~--- -- " - i —• «v/i^cj.-iJii]g- bnu pactcs mentioned above.