Lexicon LXP-5 Service Manual

Circuit
Description
Lexicon
Slave Instruction
Fetch Cycle There are three different periods where the Master Z80’s request to gain
y access to the Slave Bus is honored. The first is when Slave Z80 reset (SRST)
has been asserted. In this case the Master Z80 gains immediate access with
no wait states. The other two periods occur while the Slave Z80 is performing
either an instruction fetch or an interrupt acknowledge. Timing for these two
conditions are illustrated and explained below.
ZCLK
MSREQ/
MWAIT/
MACC/
SDB 0-7
A The MasterZ80 requests Stave Access
by asserting MSREQ/
B MWAIT/ is as serted to keep the Master
Z80 in a wait state until the Refresh
window occurs.
C SMI/ indicates Slave Z80 instruction
Fetch period.
D Instruction code is read from the 8-bit
data bus.
E If MSREQ/ is asserted during the sec¬
ond T state of Instruction Fetch period
(SMI/), the Master Z80 is in sync with
the Slave Z80 Refresh period and no
wait states will occur.
F The rising edge of SMI/ indicates
the beginning of Slave Z80 Refresh
period, which is the Slave Bus access
window.
G The Refresh access window occurs
for the last two T states during a Slave
Z80 Instruction Fetch cycle. If
MSREQ/ has been previously as¬
serted, MACC/ will go low to enable
Slave Bus buffers for the Master Z80,
allowing it access to Slave RAM or
Lexichip WCS.
H During this Refresh period, the Slave
Z80 data lines are placed in a high
impedance state. The Master Z80
is then allowed access to the 8-bit data
bus for a read or write operation.
I MWAIT/ goes low for the 4th T state of
the Slave Instruction Fetch. If the Mas¬
ter Z80 has already gained access to
the Slave Bus at this point this MWAIT/
will be ignored. If MSREQ/ is activated
just after D, this wait signal will be
acknowledged, and the Master proces¬
sor will insert waits until the next Re¬
fresh period.
J At the end of Slave Refresh Access,
MACC/ is returned to a logical high,
which removes Master Z80 from the
Slave Bus.
3-14

Lexicon LXP-5 Specifications

General

Brand	Lexicon
Model	LXP-5
Category	Recording Equipment
Language	English