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YABUS.Z80RTC

A board 55mm × 65mm mounted in place of Z80CPU. There's extra socket for Z80CPU. So the /IORQ signal outgoing to the computer can be locked by YAMOD. There's also input for external /IODIS signal (from expansion connector). The YABUS slot is buffered.

To connect a YAMOD, the female DIN slot with long pins (13mm) should be used.

Also, in Sam Coupé vertical wires can be used to connect YABUS.BEND. By experimenting with the wire length and angle the YAMOD (e.g. YAMOD.AYLPT or YAMOD.ZXINPUT) can be positioned under keyboard with the slots outgoing to the back surface.

Buffered YABUS allows long wires, so the YABUS slots can be anywhere inside Sam.

Real Time Clock

The board can include optional Real Time Clock type 72421. Data lines are connected to D0..D3 of Z80CPU without buffer. Address lines are connected to buffered A8..A11. Lines A0..A4 are decoded for port address (=#xxxF by default). Extra low active signal is required from other decoder (/PRINT signal from Sam board or any from YABUS address decoder).

In default configuration, the RTC is compatibile to Sambus clock. Configuration for MB-02 compatibility (#03 base address) is also possible, but in version v001 this requires some changes on the board.

Mounting

The board can be mounted in two ways.

The first is precise socket in main board and wires in the YABUS.Z80RTC board. In this case the YABUS.Z80RTC can be removed and Z80CPU placed back into main board. The hight of mounted board is 7mm from board surface (14mm together with Z80CPU plugged in).

The second way is pinheads. (The Z80CPU would require a special pinhead plug to be connected without YABUS.Z80RTC.) The hight is 12mm from board top surface (and 19mm together with Z80CPU plugged in). However is much stable mechanically.

The board looks like this:

YABUS.Z80RTC board for Sam

In Sam motherboard at top side will be the expansion connector, in bottom right corner - the keyboard slot. At bottom side is the EPROM, while on the left - the ASIC.

Port priority

In the basic configuration, the YABUS slot has higher priority than Sam ports and external interfaces. For example YAMOD.AYLPT disables internal MIDI and YAMOD.ZXINPUT disables the keyboard.

It is possible to give the highest proprity to rear slot. In this case the /IORQ signal from CPU must be connected directly to pin 1A of the rear slot and the track to it must be cuted. Also, the /DBDIR signal from pin 1C of rear slot must be connected to input pin of YABUS.Z80RTC.

To get the highest priority, the external interface must force low state on /DBDIR. In normal Sambus mode, the external interface makes /DBDIR=0 only when Z80CPU reads from the port.

To force the highest priority also for writing, the external interface must give /DBDIR=0 also while writing. The Sambus must be skipped or upgraded to portfix compatibility. See portfix link below.


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Files for download

samrtc.jpg 96.3kB (2006-07-18 19:30)
YABUS.Z80RTC without YABUS slot mounted inside Sam Coupé.
empty.jpg 102.0kB (2006-06-01 23:56)
Empty YABUS.Z80RTC board mounted in Sam Coupé in precise socket.
socket.jpg 87.9kB (2006-06-01 22:47)
Z80CPU replaced by precise socket in Sam Coupé.
z80rtc1.zip 63.5kB (2006-04-03 21:41)
First board project. Eagle and Tango PCB data files.

Links to other pages



See also

Portfix
Allows to disable internal ports by external interface.

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CPC
4MB RAM
Flash ROM
To 128
Sam Coupé
SAM512
Portfix
YABUS.Z80RTC
Z80JOY
MSX
Mapper 4MB
MSX-2 SVI738
Spectrum
FlashD0
8251
AY
Eniac'owe
Dock
Gama 192
Keyboard
ROM replacer
SamRam
TC2144
To 128K
To +3
Wonder RAM
Z80JOY
ZX 4MB
ZXMUX
Timex
Memory
Timex FDD
YABUS.TF
YABUS.TF3
TI-of-TTL
ZX81
Memory

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© 2009-12-28 21:50 Jarek Adamski, http://8bit.yarek.pl