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"MTX Plus+"
Firmware Features - Usage
The
MTXPlus+ firmware includes a significant number of enhancements
over the standard Memotech MTX ROMs, but supports almost all of
the original ROM functions - the exception being the cassette
tape functions. Refer to the standard Memotech documentation for
detailed coverage of the relevant features, including :
This page describes how to use the additional features of
MTXPlus+ that are not already described in Memotech or my CFX
documents.
System Control
Register
An 8-bit control register is used to store configuration
relevant to Speculator+
(bits 0 to 3) and for the
CPU clock speed selection logic (bits
4 - 7). See the Speculator+
page for details on bits 0 to 3. This register is accessed
through I/O port 255 (FFh).
| Bit
Mapping |
MTXPlus+ Control
Register (Port FFh) |
|
|
Description |
|
|
| Speculator+
NMI_EN |
0 = disable, 1 = enable |
|
Speculator+ NMI_SEL |
0 = delayed, 1 =
immediate *** not used *** |
| Speculator+
ZX_Mode |
0 = lower 16K R/W, 1 = lower 16K R/O
|
|
Speculator+
Wait control |
|
| Software PHI Select |
LSB |
(See
clock generation page for details) |
| Software PHI Select |
|
| Software PHI Select |
|
| Software PHI Select |
MSB |
|
At Reset, the system defaults to a clock
frequency of 4Mhz and bits D7 to D4 of the Control Register are
cleared.
CPU Speed Detection & Control
When
the system is booted, the MTXPlus+ support ROM runs
a speed detection routine and reports the current
clock speed in MHz.
Once the system is executing the BASIC ROM, the
speed can be switched thorough software by writing
to the system control I/O port (255) and additional
BASIC commands can be used to read the CPU clock
frequency and set the value of the internal CPU
clock multiplier. The Z180S version of the CPU board
supports the clock doubling features of the Z180S
and starts up in un-doubled mode, see the
CPU V3 page
for details of the clock doubling features
CPU Clock Speed Control from BASIC
| Description |
|
Applies to |
| Report the current
CPU speed and, for the Z180S only, the status of the clock multiplier |
USER SPEED |
Z80 & Z180S |
| |
|
|
| For the Z80, the USER
SPEED command can be used to set the clock rate
to any 1 of the 16 available frequencies from 4 to 16
MHz. |
USER SPEED [int]
where int = 0 .. 15 |
Z80 |
| |
|
|
| For the Z180S, USER
commands can be used to set the clock multiplier to
half, single or double speed, they have no effect on the
Z80 board where the clock multiplier does not exisit. |
USER HALF |
Z180S |
| USER SINGLE |
Z180S |
| USER TURBO |
Z180S |
| |
|
|
Speed Selection Using I/O Port FFh
In addition to using the new BASIC
USER SPEED command, the user can also write to I/O
port 255 (FFh) directly to change the system clock
frequency.
Real Time Clock
For an
overview of the RTC, please see the
I/O Ports page and for a full description of the
RTC's registers
and status bytes, see the Dallas
Semiconductor
DS12887
datasheet.
Date & Time Functions
To simplify
communication with the RTC, additional commands have
been added to MTXPlus+ BASIC.
|
Set RTC Date
& Time |
| USER SETDATE |
"dd/mmyy" |
| USER SETTIME |
"hh:mm:ss" |
| Read RTC
Date & Time |
| USER GETDATE |
|
| USER GETTIME |
|
| Update MTX
Clock from the RTC |
| USER SETCLOCK |
|
Slow CPU Clock Source
For diagnostic purposes, it is possible
to run MTXPlus+ with an ultra-slow CPU
clock, this is derived from the Square
Wave Output of the RTC and can be set to
a range of values between 2Hz and 8,192
kHz, defined by the lower 4 bits of
Status Register A. (These bits also
setup the periodic interrupt rate to
generate a CPU interrupt for user
programs - this function is not used in
MTXPlus+).
Note:
Even at the maximum rate of 8Khz, the
slow clock is unlikely to be useful if
the only method of monitoring the system
is through the normal video output. The
system would be running some 500 times
slower than design and take far too long to display
meaningful output to the screen. The
slow clock in designed to be used in
tandem with the Bus Diagnostic Card,
probably with a clock setting of 2
or 4 Hz.
| Status
Register A |
| Bit7 |
Bit6 |
Bit5 |
Bit4 |
Bit3 |
Bit2 |
Bit1 |
Bit0 |
| UIP |
DV2 |
DV1 |
DV0 |
RS3 |
RS2 |
RS1 |
RS0 |
|
|
Status Register A |
Periodic |
SQW |
|
RS3 |
RS2 |
RS1 |
RS0 |
Interrupt Rate |
Frequency |
|
See
DS12887
datasheet for all available values |
| 0 |
0 |
0 |
0 |
None |
None |
| 0 |
0 |
1 |
1 |
122.070 us |
8.192
kHz |
| 1 |
1 |
1 |
0 |
250 ms |
4 Hz |
| 1 |
1 |
1 |
1 |
500 ms |
2 Hz |
Status Register A is also used
to start & stop the RTC and
stores a flag (bit 7, read only)
signifying when an update will
soon occur (Update
In Progress).
To update the status
register, the a pattern of "010"
should also be written to bits
6..4 to ensure that the RTC is
running. For example, to set a
4Hz SQW frequency, a bit pattern
of x0101110 should be set (46d) |
Setup write to Register A |
| OUT 112,
10 |
|
Update SQW frequency bits |
| OUT 113,
46 |
| |
| |
|
| Status
Register B |
| Bit7 |
Bit6 |
Bit5 |
Bit4 |
Bit3 |
Bit2 |
Bit1 |
Bit0 |
| SET |
N/A for MTXPlus+ |
SQWE |
DM |
24/12 |
DSE |
| SET |
0 when normal updates are
occurring, 1 when setting
date/time |
| SQWE |
Square Wave Enable (1 =
enabled) |
| DM |
Date Mode (1 = Binary, 0 =
BCD), Binary mode used in
MTXPlus+ |
| 24/12 |
Hours format (1 = 24 hours,
0 = 12 hours), 24 hour mode used
in MTXPlus+ |
| DSE |
Daylight Savings Enable (1 =
DST enabled, 0 = DST disabled) |
|
Status Register B is used to
control various RTC functions,
as shown in the table above, not
all are relevant to MTXPlus+.
To update the SQW enable
bit, the user should first read
the current value in the
register to preserve the current
settings before writing a new
value to the register.
Bits
7, 6, 5 and 4 should be zero
Only update the SQWE bit,
i.e., the new value should be
the old value, 'OR'ed with 8 |
Setup access to Register B |
| OUT 112,
11 |
|
Read current register value |
| LET X =
INP (113) (e.g. x =2) |
|
Setup access to Register B |
| Only
update SQWE (bit 3) |
| e.g. OUT
113, (2+8) |
| |
| |
|
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