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--- qlwiki:rom_port [2018/05/13 17:52] – Minor correction, tracks not pins in table header. normandunbar
+++ qlwiki:rom_port [2023/08/25 12:22] (current) – external edit 127.0.0.1
@@ Line 72: / Line 72: @@
 **WARNING**: Never plug or unplug a ROM cartridge while the QL power is on.
+==== MBM27128-25 Details ====
+I'm unaware if the MBM27128-25 chip is the same EPROM used in every QL ROM cartridge, but just in case, here are some details about it, and how it needs to be set up to be read. Programming is not something I've ever done with EPROMs, so I leave those details to others.
+<code>
+        ------v------
+VPP   o|  1       28 |o   VCC
+A12   o|  2       27 |o   Pbar
+A7    o|  3       26 |o   A13
+A6    o|  4       25 |o   A8
+A5    o|  5       24 |o   A9
+A4    o|  6       23 |o   A11
+A3    o|  7       22 |o   Qbar
+A2    o|  8       21 |o   A10
+A1    o|  9       20 |o   Ebar
+A0    o| 10       19 |o   D7
+D0    o| 11       18 |o   D6
+D1    o| 12       17 |o   D5
+D2    o| 13       16 |o   D4
+VSS   o| 14       15 |o   D3
+        -------------
+    PinOut for MBM27128-25
+</code>
+Notes:
+  * Qbar, Pbar and Ebar are active low.
+  * Qbar enables the data output. When pulled low, data can be read from the data lines D0-D7.
+  * Pbar controls the chip programming. You'll need an EPROM programmer to make use of this.
+  * Ebar enables the chip itself. When high, the chip is disabled, when low, the chip is enabled.
+  * VSS is ground.
+  * VCC is 5v nominal but never higher than 7v absolute maximum (above VSS).
+  * VPP should be the same as VSS when reading data. 5v.
+  * D0-D7 are referred to as Q0-Q7 on some data sheets. Q meaning output.
+From the data sheet for a MBM27128-25, to read data, the following should be carried out:
+Initially:
+  * Connect VSS to ground.
+  * Connect VPP, VCC and Pbar to +5v.
+In a loop to read various addresses:
+  * Connect Ebar to +5v.
+  * Set up the required address to be read, on the address lines A0-A15.
+  * Connect Ebar to ground to enable data output.
+  * In the case of the MBM27128-25, data will be stable within 250 nano seconds, maximum. The MBM27128-20 is stable within 200 nano seconds and the MBM27128-30 within 300 nano seconds.
+  * Read the data byte from data lines D0-D7.
+The data sheet does not state how long it takes for the address lines to become stable, there might need to be a delay, or maybe the time it takes to bring Qbar low is all the delay required.