Lexicon 960L Service Manual page 39

Lexicon
Tests the Dual Port RAM, associated with a specific Z80, via the 56301 This command performs a memory
test on the dual port RAM (DPRAM) associated with a particular Z80 on a particular reverb card. Values of
0, 0xFF, 0xAA and 0x55 are written to the DPRAM via the 56301 then read back and confirmed An address
test is also run that writes each address value into its associated memory location (address 29 has the
value 29 written into it, address 30 has the value 30 written into it, etc...). This test confirms that the 56301
can access all of the DPRAM memory.
If this test fails, there is a problem with the address, data, or control lines between the 56301 and the
DPRAM.
Parameters:
CardID:
This number selects which reverb card to test. Legal values are 0 and 1, since only two reverb cards will be
supported. If only one card is present use the number 0.
Z80Id:
This specifies which DPRAM associated with a particular Z80 on the card to test. Legal Values are 0 and 1.
NumRepeats:
This optional parameter specifies how many times to run the test. A value of 0 runs the test indefinitely (until
a key is pressed). Dots are shown on the display to indicate that the test is still running.
56301 to Z80 Test:
The syntax for the 56301 to Z80 test is: 56kToZ80CmdTest CardId Z80ID [NumRepeats].
Tests the 56301's ability to notify the Z80 of a command.
This command tests the ability of the 56301 to notify the Z80 of a new command. The 56301 processor
sends messages to the Z80s through the DPRAM. The DPRAMs have a special feature that facilitates this;
the last two addresses of the DPRAM trigger the INT pins when written to. When address 7FE is written to
from the right (56301) side, the INTL pin goes low. If the Z80 then writes to the same address, the line
returns high. If the Z80 writes to address 7FF, the INTR pin goes low. If the 56301 then writes to the same
address, the line returns high.
The 56301 writes data to address 7FE of the DPRAM driving the INTL line low. The INTL line feeds pin 54
(M_R) of the Lexichip3, which can then be read (via the Lexichip3) by the Z80. Before any of this, however,
a tiny program is loaded into the DPRAM for the Z80 to run, which has the Z80 constantly reading address
0x3B18 in the Lexichip3 and checking for a low on bit 6 of the data it gets back. Address 0x3B18 is the
location in the Lexichip3 in which the INTL pin's state is stored at bit 6. When bit 6 goes low, the program
writes 0xAA into address 0x0014 of the DPRAM which the 56301 reads to confirm that the message was
received. If the value at address 0x0014 of the DPRAM is not 0xAA, then the Z80 did not detect a message
from the 56301 and the test fails.
In order for this test to pass, the INTL line must be connected to pin 54 of the Lexichip3. The Z80 must also
be able to read from the Lexichip3's memory so the address and data lines between the Z80 and the
Lexichip3 must be intact. Obviously, the mechanism within the DPRAM that triggers the INTL line going low
must be functional for the test to pass.
Parameters:
CardID:
This number selects which reverb card to test. Legal values are 0 and 1, since only two reverb cards will be
supported. If only one card is present use the number 0.
Z80Id:
This specifies which DPRAM associated with a particular Z80 on the card to test. Legal Values are 0 and 1.
NumRepeats:
This optional parameter specifies how many times to run the test. A value of 0 runs the test indefinitely (until
a key is pressed). Dots are shown on the display to indicate that the test is still running.
6-7