{"id":109,"date":"2011-09-24T11:51:57","date_gmt":"2011-09-24T09:51:57","guid":{"rendered":"http:\/\/lazlo.de\/?p=109"},"modified":"2013-04-20T01:35:45","modified_gmt":"2013-04-19T23:35:45","slug":"external-memory-board","status":"publish","type":"post","link":"http:\/\/lazlo.de\/blog\/2011\/09\/24\/external-memory-board\/","title":{"rendered":"external memory board"},"content":{"rendered":"<p>Just before writing my last post, I started building another board in order to supply my ATmega128 with 64Kbytes of external memory (in fact the so called &#8220;XMEM&#8221; feature was one of the reasons I bought that chip).<\/p>\n<p>The board is designed for a 28 pin S-RAM IC (<a title=\"Hitachi HM6264 datasheet\" href=\"http:\/\/www.datasheetarchive.com\/dl\/Datasheets-13\/DSA-247725.pdf\" target=\"_blank\">Hitachi HM6264<\/a>) that can be connected to a micro controller supporting external memory (like the ATmega128 or ATmega162) using three 10 pin headers. The first header is used for the multiplexed lower address\/IO bits (port A on micro controller), the second for dedicated upper address bits (port C) and the last for read\/write strobe and address latch enable (port G). All headers share two common last pins: GND (9) and VCC (10). The only thing required except for the S-RAM itself, some pin headers and a 100uF ceramic capacitor is a octal latch IC (74AHC573) that will allow for multiplexing the shared lower address\/IO lines.<\/p>\n<p><strong>NOTE<\/strong><\/p>\n<p>After looking up the &#8220;Address Latch Requirements&#8221; section in the <a title=\"ATmega128 datasheet\" href=\"http:\/\/www.atmel.com\/atmel\/acrobat\/doc2467.pdf\" target=\"_blank\">ATmega128 datasheet<\/a> turns out that when the micro controller is operated above 8MHz (mine has a 16MHz crystal) the 74HC573 (the IC I have) does not meet requirements but a 74AHC573 would do. I guess I will put in a 8MHz crystal until I can get hold of a 74AHC573.<\/p>\n<p><a href=\"http:\/\/lazlo.de\/wp-content\/uploads\/2011\/09\/mem-sram-64k-top-P1070573.jpg\"><div id='gallery-1' class='gallery galleryid-109 gallery-columns-2 gallery-size-thumbnail'><figure class='gallery-item'>\n\t\t\t<div class='gallery-icon landscape'>\n\t\t\t\t<a href='http:\/\/lazlo.de\/blog\/wp-content\/uploads\/2011\/09\/mem-sram-64k-top-P1070573.jpg'><img loading=\"lazy\" decoding=\"async\" width=\"150\" height=\"150\" src=\"http:\/\/lazlo.de\/blog\/wp-content\/uploads\/2011\/09\/mem-sram-64k-top-P1070573-150x150.jpg\" class=\"attachment-thumbnail size-thumbnail\" alt=\"\" \/><\/a>\n\t\t\t<\/div><\/figure><figure class='gallery-item'>\n\t\t\t<div class='gallery-icon landscape'>\n\t\t\t\t<a href='http:\/\/lazlo.de\/blog\/wp-content\/uploads\/2011\/09\/mem-sram-64k-bottom-P1070571.jpg'><img loading=\"lazy\" decoding=\"async\" width=\"150\" height=\"150\" src=\"http:\/\/lazlo.de\/blog\/wp-content\/uploads\/2011\/09\/mem-sram-64k-bottom-P1070571-150x150.jpg\" class=\"attachment-thumbnail size-thumbnail\" alt=\"\" \/><\/a>\n\t\t\t<\/div><\/figure>\n\t\t<\/div>\n<\/p>\n<p><\/a><\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p><strong>Download<\/strong><\/p>\n<ul>\n<li><a href=\"http:\/\/lazlo.de\/wp-content\/uploads\/2011\/09\/mem-sram-64k-sch.pdf\">schematic (PDF)<\/a><\/li>\n<li><a href=\"http:\/\/lazlo.de\/wp-content\/uploads\/2011\/09\/mem-sram-64k-brd.pdf\">board layout (PDF)<\/a><\/li>\n<li><a href=\"http:\/\/lazlo.de\/wp-content\/uploads\/2011\/09\/mem-sram-64k.zip\">schematic (.sch) and board layout (.brd) files as .zip archive<\/a><\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Just before writing my last post, I started building another board in order to supply my ATmega128 with 64Kbytes of external memory (in fact the so called &#8220;XMEM&#8221; feature was one of the reasons I bought &hellip; <a class=\"more-link\" href=\"http:\/\/lazlo.de\/blog\/2011\/09\/24\/external-memory-board\/\">More<span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[114,102],"tags":[9,121,82,6,30,88,86,89,87,85,10],"class_list":["post-109","post","type-post","status-publish","format-standard","hentry","category-hardware-work","category-work","tag-avr","tag-circuit","tag-development","tag-embedded","tag-hardware","tag-memory","tag-pcb","tag-photo","tag-ram","tag-schematic","tag-xmem"],"_links":{"self":[{"href":"http:\/\/lazlo.de\/blog\/wp-json\/wp\/v2\/posts\/109","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/lazlo.de\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/lazlo.de\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/lazlo.de\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/lazlo.de\/blog\/wp-json\/wp\/v2\/comments?post=109"}],"version-history":[{"count":52,"href":"http:\/\/lazlo.de\/blog\/wp-json\/wp\/v2\/posts\/109\/revisions"}],"predecessor-version":[{"id":738,"href":"http:\/\/lazlo.de\/blog\/wp-json\/wp\/v2\/posts\/109\/revisions\/738"}],"wp:attachment":[{"href":"http:\/\/lazlo.de\/blog\/wp-json\/wp\/v2\/media?parent=109"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/lazlo.de\/blog\/wp-json\/wp\/v2\/categories?post=109"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/lazlo.de\/blog\/wp-json\/wp\/v2\/tags?post=109"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}